XML 146 R126.htm IDEA: XBRL DOCUMENT v3.8.0.1
Schedule III - Real Estate and Accumulated Depreciation (Details)
 12 Months Ended
Dec. 31, 2017
USD ($)
ApartmentUnit
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Real Estate And Accumulated Depreciation Abstract        
Accumulated Depreciation $ (6,040,378,000) $ (5,360,389,000) $ (6,084,616,000) $ (5,432,805,000)
100 K Street [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 15,600,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 30,003,159      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2017, Land 15,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 30,003,159      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 45,603,159      
Accumulated Depreciation 0      
Investment in Real Estate, Net 45,603,159      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
140 Riverside Boulevard [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 354      
Initial Cost to Company, Land $ 103,539,100      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 94,082,725      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 8,607,947      
Gross Amount Carried at close of period 12/31/2017, Land 103,539,100      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 102,690,672      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 206,229,772      
Accumulated Depreciation (44,828,691)      
Investment in Real Estate, Net 161,401,081      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
160 Riverside Boulevard [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 455      
Initial Cost to Company, Land $ 139,933,500      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 190,964,745      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 14,965,349      
Gross Amount Carried at close of period 12/31/2017, Land 139,933,500      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 205,930,094      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 345,863,594      
Accumulated Depreciation (89,280,987)      
Investment in Real Estate, Net 256,582,607      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
170 Amsterdam [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 236      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 112,081,768      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 135,722      
Gross Amount Carried at close of period 12/31/2017, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 112,217,490      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 112,217,490      
Accumulated Depreciation (11,505,275)      
Investment in Real Estate, Net 100,712,215      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
175 Kent [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Brooklyn, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 113      
Initial Cost to Company, Land $ 22,037,831      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 53,962,169      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,534,419      
Gross Amount Carried at close of period 12/31/2017, Land 22,037,831      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 55,496,588      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 77,534,419      
Accumulated Depreciation (14,450,457)      
Investment in Real Estate, Net 63,083,962      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
180 Montague (fka Brooklyn Heights) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Brooklyn, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 193      
Initial Cost to Company, Land $ 32,400,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 92,675,228      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,547,996      
Gross Amount Carried at close of period 12/31/2017, Land 32,400,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 96,223,224      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 128,623,224      
Accumulated Depreciation (20,134,074)      
Investment in Real Estate, Net 108,489,150      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
180 Riverside Boulevard [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 516      
Initial Cost to Company, Land $ 144,968,250      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 138,346,681      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 12,874,009      
Gross Amount Carried at close of period 12/31/2017, Land 144,968,250      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 151,220,690      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 296,188,940      
Accumulated Depreciation (67,181,115)      
Investment in Real Estate, Net 229,007,825      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
1111 Belle Pre (fka The Madison) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Alexandria, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 360      
Initial Cost to Company, Land $ 18,937,702      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 94,759,478      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 148,954      
Gross Amount Carried at close of period 12/31/2017, Land 18,937,702      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 94,908,432      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 113,846,134      
Accumulated Depreciation (17,565,898)      
Investment in Real Estate, Net 96,280,236      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
1210 Mass [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 144      
Initial Cost to Company, Land $ 9,213,513      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 36,559,189      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,403,479      
Gross Amount Carried at close of period 12/31/2017, Land 9,213,513      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 38,962,668      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 48,176,181      
Accumulated Depreciation (16,940,349)      
Investment in Real Estate, Net 31,235,832      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
1401 E. Madison [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 10,401,958      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 7,932,051      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2017, Land 10,401,958      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 7,932,051      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 18,334,009      
Accumulated Depreciation 0      
Investment in Real Estate, Net 18,334,009      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
1500 Mass Ave [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 556      
Initial Cost to Company, Land $ 54,638,298      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 40,361,702      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 14,859,237      
Gross Amount Carried at close of period 12/31/2017, Land 54,638,298      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 55,220,939      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 109,859,237      
Accumulated Depreciation (24,493,269)      
Investment in Real Estate, Net 85,365,968      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
1800 Oak (fka Rosslyn) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 314      
Initial Cost to Company, Land $ 31,400,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 109,005,734      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,172,464      
Gross Amount Carried at close of period 12/31/2017, Land 31,400,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 112,178,198      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 143,578,198      
Accumulated Depreciation (23,997,938)      
Investment in Real Estate, Net 119,580,260      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
2201 Pershing Drive [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 188      
Initial Cost to Company, Land $ 11,321,198      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 49,674,175      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,176,089      
Gross Amount Carried at close of period 12/31/2017, Land 11,321,198      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 51,850,264      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 63,171,462      
Accumulated Depreciation (11,636,674)      
Investment in Real Estate, Net 51,534,788      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
2201 Wilson [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 219      
Initial Cost to Company, Land $ 21,900,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 78,724,663      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,493,731      
Gross Amount Carried at close of period 12/31/2017, Land 21,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 82,218,394      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 104,118,394      
Accumulated Depreciation (17,067,795)      
Investment in Real Estate, Net 87,050,599      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
M St 2400 [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 359      
Initial Cost to Company, Land $ 30,006,593      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 114,013,785      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,296,314      
Gross Amount Carried at close of period 12/31/2017, Land 30,006,593      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 118,310,099      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 148,316,692      
Accumulated Depreciation (49,487,043)      
Investment in Real Estate, Net 98,829,649      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
249 Third Street (fka Kendall Square II) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Cambridge, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 4,603,326      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 4,330,982      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2017, Land 4,603,326      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 4,330,982      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 8,934,308      
Accumulated Depreciation 0      
Investment in Real Estate, Net 8,934,308      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
315 on A [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Boston, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 202      
Initial Cost to Company, Land $ 14,450,070      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 115,824,930      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 623,402      
Gross Amount Carried at close of period 12/31/2017, Land 14,450,070      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 116,448,332      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 130,898,402      
Accumulated Depreciation (14,489,301)      
Investment in Real Estate, Net 116,409,101      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
340 Fremont [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Francisco, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 348      
Initial Cost to Company, Land $ 42,000,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 247,606,631      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,551      
Gross Amount Carried at close of period 12/31/2017, Land 42,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 247,611,182      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 289,611,182      
Accumulated Depreciation (14,159,585)      
Investment in Real Estate, Net 275,451,597      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
3003 Van Ness [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 625      
Initial Cost to Company, Land $ 56,300,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 141,191,580      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,117,966      
Gross Amount Carried at close of period 12/31/2017, Land 56,300,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 146,309,546      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 202,609,546      
Accumulated Depreciation (33,088,622)      
Investment in Real Estate, Net 169,520,924      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
45 Worthington [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Boston, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 2,349,475      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2017, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 2,349,475      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 2,349,475      
Accumulated Depreciation 0      
Investment in Real Estate, Net 2,349,475      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
420 East 80th Street [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 155      
Initial Cost to Company, Land $ 39,277,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 23,026,984      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,675,293      
Gross Amount Carried at close of period 12/31/2017, Land 39,277,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 27,702,277      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 66,979,277      
Accumulated Depreciation (13,594,720)      
Investment in Real Estate, Net 53,384,557      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
425 Mass [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 559      
Initial Cost to Company, Land $ 28,150,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 138,600,000      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,974,856      
Gross Amount Carried at close of period 12/31/2017, Land 28,150,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 142,574,856      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 170,724,856      
Accumulated Depreciation (44,144,101)      
Investment in Real Estate, Net 126,580,755      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
455 I Street [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 174      
Initial Cost to Company, Land $ 11,941,407      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 61,030,786      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2017, Land 11,941,407      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 61,030,786      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 72,972,193      
Accumulated Depreciation (1,082,263)      
Investment in Real Estate, Net 71,889,930      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
4885 Edgemoor Lane [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Bethesda, MD      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 1,958,883      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2017, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 1,958,883      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 1,958,883      
Accumulated Depreciation 0      
Investment in Real Estate, Net 1,958,883      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
4701 Willard [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Chevy Chase, MD      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 517      
Initial Cost to Company, Land $ 76,921,130      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 153,947,682      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 29,902,775      
Gross Amount Carried at close of period 12/31/2017, Land 76,921,130      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 183,850,457      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 260,771,587      
Accumulated Depreciation (50,471,131)      
Investment in Real Estate, Net 210,300,456      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
4th and Hill [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 13,131,456      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 13,790,436      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2017, Land 13,131,456      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 13,790,436      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 26,921,892      
Accumulated Depreciation 0      
Investment in Real Estate, Net 26,921,892      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
600 Washington [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 135      
Initial Cost to Company, Land $ 32,852,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 43,140,551      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 870,871      
Gross Amount Carried at close of period 12/31/2017, Land 32,852,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 44,011,422      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 76,863,422      
Accumulated Depreciation (19,355,357)      
Investment in Real Estate, Net 57,508,065      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
660 Washington [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Boston, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 420      
Initial Cost to Company, Land $ 106,100,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 166,311,679      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,888,133      
Gross Amount Carried at close of period 12/31/2017, Land 106,100,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 169,199,812      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 275,299,812      
Accumulated Depreciation (35,392,580)      
Investment in Real Estate, Net 239,907,232      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
70 Greene [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Jersey City, NJ      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 480      
Initial Cost to Company, Land $ 28,108,899      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 236,763,553      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,657,070      
Gross Amount Carried at close of period 12/31/2017, Land 28,108,899      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 238,420,623      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 266,529,522      
Accumulated Depreciation (65,784,128)      
Investment in Real Estate, Net 200,745,394      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
71 Broadway [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 238      
Initial Cost to Company, Land $ 22,611,600      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 77,492,171      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 14,064,394      
Gross Amount Carried at close of period 12/31/2017, Land 22,611,600      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 91,556,565      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 114,168,165      
Accumulated Depreciation (43,472,173)      
Investment in Real Estate, Net 70,695,992      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
77 Bluxome [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Francisco, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 102      
Initial Cost to Company, Land $ 5,249,124      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 18,609,876      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 402,201      
Gross Amount Carried at close of period 12/31/2017, Land 5,249,124      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 19,012,077      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 24,261,201      
Accumulated Depreciation (5,178,232)      
Investment in Real Estate, Net 19,082,969      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
77 Park Avenue (fka Hoboken) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Hoboken, NJ      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 301      
Initial Cost to Company, Land $ 27,900,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 168,992,440      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,060,186      
Gross Amount Carried at close of period 12/31/2017, Land 27,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 175,052,626      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 202,952,626      
Accumulated Depreciation (35,032,130)      
Investment in Real Estate, Net 167,920,496      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
777 Sixth [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 294      
Initial Cost to Company, Land $ 65,352,706      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 65,747,294      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,136,354      
Gross Amount Carried at close of period 12/31/2017, Land 65,352,706      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 68,883,648      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 134,236,354      
Accumulated Depreciation (26,152,102)      
Investment in Real Estate, Net 108,084,252      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
88 Hillside [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Daly City, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 95      
Initial Cost to Company, Land $ 7,786,800      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 31,587,325      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,479,165      
Gross Amount Carried at close of period 12/31/2017, Land 7,786,800      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 34,066,490      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 41,853,290      
Accumulated Depreciation (8,687,690)      
Investment in Real Estate, Net 33,165,600      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
855 Brannan [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Francisco, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 41,363,921      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 255,551,895      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 249      
Gross Amount Carried at close of period 12/31/2017, Land 41,363,921      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 255,552,144      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 296,916,065      
Accumulated Depreciation (1,845,523)      
Investment in Real Estate, Net 295,070,542      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Acton Courtyard [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Berkeley, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 71      
Initial Cost to Company, Land $ 5,550,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 15,785,509      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 215,312      
Gross Amount Carried at close of period 12/31/2017, Land 5,550,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 16,000,821      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 21,550,821      
Accumulated Depreciation (6,583,929)      
Investment in Real Estate, Net 14,966,892      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Alban Towers [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 229      
Initial Cost to Company, Land $ 18,900,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 89,794,201      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,280,842      
Gross Amount Carried at close of period 12/31/2017, Land 18,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 93,075,043      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 111,975,043      
Accumulated Depreciation (18,879,861)      
Investment in Real Estate, Net 93,095,182      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Acappella [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Pasadena, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 143      
Initial Cost to Company, Land $ 5,839,548      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 29,360,452      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,048,185      
Gross Amount Carried at close of period 12/31/2017, Land 5,839,548      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 31,408,637      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 37,248,185      
Accumulated Depreciation (10,041,304)      
Investment in Real Estate, Net 27,206,881      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Altitude [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 545      
Initial Cost to Company, Land $ 43,783,485      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 147,964,006      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 61,899      
Gross Amount Carried at close of period 12/31/2017, Land 43,783,485      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 148,025,905      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 191,809,390      
Accumulated Depreciation (8,474,037)      
Investment in Real Estate, Net 183,335,353      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Alton, The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Irvine, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 344      
Initial Cost to Company, Land $ 11,049,027      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 95,745,832      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,433      
Gross Amount Carried at close of period 12/31/2017, Land 11,049,027      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 95,750,265      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 106,799,292      
Accumulated Depreciation (3,470,417)      
Investment in Real Estate, Net 103,328,875      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Arbor Terrace [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Sunnyvale, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 175      
Initial Cost to Company, Land $ 9,057,300      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 18,483,642      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,806,335      
Gross Amount Carried at close of period 12/31/2017, Land 9,057,300      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 26,289,977      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 35,347,277      
Accumulated Depreciation (15,015,023)      
Investment in Real Estate, Net 20,332,254      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Alborada [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Fremont, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 442      
Initial Cost to Company, Land $ 24,310,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 59,214,129      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 9,118,031      
Gross Amount Carried at close of period 12/31/2017, Land 24,310,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 68,332,160      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 92,642,160      
Accumulated Depreciation (39,048,480)      
Investment in Real Estate, Net 53,593,680      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Artech Building [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Berkeley, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 27      
Initial Cost to Company, Land $ 1,642,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 9,152,518      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 493,478      
Gross Amount Carried at close of period 12/31/2017, Land 1,642,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 9,645,996      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 11,287,996      
Accumulated Depreciation (3,706,713)      
Investment in Real Estate, Net 7,581,283      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Artisan on Second [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 118      
Initial Cost to Company, Land $ 8,000,400      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 36,074,600      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 880,695      
Gross Amount Carried at close of period 12/31/2017, Land 8,000,400      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 36,955,295      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 44,955,695      
Accumulated Depreciation (10,464,974)      
Investment in Real Estate, Net 34,490,721      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Artistry Emeryville (fka Emeryville) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Emeryville, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 261      
Initial Cost to Company, Land $ 12,300,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 61,466,267      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,320,134      
Gross Amount Carried at close of period 12/31/2017, Land 12,300,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 65,786,401      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 78,086,401      
Accumulated Depreciation (14,859,853)      
Investment in Real Estate, Net 63,226,548      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Atelier [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Brooklyn, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 120      
Initial Cost to Company, Land $ 32,401,680      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 47,135,432      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 276,205      
Gross Amount Carried at close of period 12/31/2017, Land 32,401,680      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 47,411,637      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 79,813,317      
Accumulated Depreciation (4,883,375)      
Investment in Real Estate, Net 74,929,942      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Avenue Two [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Redwood City, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 123      
Initial Cost to Company, Land $ 7,995,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 18,005,000      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,027,422      
Gross Amount Carried at close of period 12/31/2017, Land 7,995,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 20,032,422      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 28,027,422      
Accumulated Depreciation (5,941,287)      
Investment in Real Estate, Net 22,086,135      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Azure [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Francisco, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 273      
Initial Cost to Company, Land $ 32,855,115      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 152,627,844      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 141,813      
Gross Amount Carried at close of period 12/31/2017, Land 32,855,115      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 152,769,657      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 185,624,772      
Accumulated Depreciation (13,532,368)      
Investment in Real Estate, Net 172,092,404      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Bella Fontaine [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Marina Del Rey, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 102      
Initial Cost to Company, Land $ 9,098,808      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 28,701,192      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 771,386      
Gross Amount Carried at close of period 12/31/2017, Land 9,098,808      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 29,472,578      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 38,571,386      
Accumulated Depreciation (7,870,020)      
Investment in Real Estate, Net 30,701,366      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Bay Hill [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Long Beach, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 160      
Initial Cost to Company, Land $ 7,600,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 27,437,239      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,327,400      
Gross Amount Carried at close of period 12/31/2017, Land 7,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 30,764,639      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 38,364,639      
Accumulated Depreciation (14,290,928)      
Investment in Real Estate, Net 24,073,711      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Breakwater at Marina Del Rey [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Marina Del Rey, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 224      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 73,189,262      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,974,133      
Gross Amount Carried at close of period 12/31/2017, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 75,163,395      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 75,163,395      
Accumulated Depreciation (17,008,793)      
Investment in Real Estate, Net 58,154,602      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Beatrice, The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 302      
Initial Cost to Company, Land $ 114,351,405      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 165,648,595      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,368,317      
Gross Amount Carried at close of period 12/31/2017, Land 114,351,405      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 167,016,912      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 281,368,317      
Accumulated Depreciation (40,862,593)      
Investment in Real Estate, Net 240,505,724      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Briarwood (CA) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Sunnyvale, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 192      
Initial Cost to Company, Land $ 9,991,500      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 22,247,278      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,973,927      
Gross Amount Carried at close of period 12/31/2017, Land 9,991,500      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 26,221,205      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 36,212,705      
Accumulated Depreciation (16,926,737)      
Investment in Real Estate, Net 19,285,968      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Belle Arts Condominium Homes, LLC [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Bellevue, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 1      
Initial Cost to Company, Land $ 63,158      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 236,157      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,098      
Gross Amount Carried at close of period 12/31/2017, Land 63,158      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 238,255      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 301,413      
Accumulated Depreciation (75,056)      
Investment in Real Estate, Net 226,357      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Bridford Lakes Two [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Greensboro, NC      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 200,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 0      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2017, Land 200,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 200,000      
Accumulated Depreciation 0      
Investment in Real Estate, Net 200,000      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Brooklyner (fka 111 Lawrence) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Brooklyn, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 490      
Initial Cost to Company, Land $ 40,099,922      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 221,438,631      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,859,816      
Gross Amount Carried at close of period 12/31/2017, Land 40,099,922      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 224,298,447      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 264,398,369      
Accumulated Depreciation (53,947,636)      
Investment in Real Estate, Net 210,450,733      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
C on Pico [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 94      
Initial Cost to Company, Land $ 17,125,766      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 28,074,234      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 63,493      
Gross Amount Carried at close of period 12/31/2017, Land 17,125,766      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 28,137,727      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 45,263,493      
Accumulated Depreciation (2,749,575)      
Investment in Real Estate, Net 42,513,918      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Carlyle Mill [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Alexandria, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 317      
Initial Cost to Company, Land $ 10,000,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 51,367,913      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 8,305,516      
Gross Amount Carried at close of period 12/31/2017, Land 10,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 59,673,429      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 69,673,429      
Accumulated Depreciation (30,572,284)      
Investment in Real Estate, Net 39,101,145      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Cascade [Domain]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 477      
Initial Cost to Company, Land $ 23,751,564      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 145,844,715      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2017, Land 23,751,564      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 145,844,715      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 169,596,279      
Accumulated Depreciation (2,364,423)      
Investment in Real Estate, Net 167,231,856      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Centennial (fka Centennial Court & Centennial Tower) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 408      
Initial Cost to Company, Land $ 9,700,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 70,080,378      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 11,471,751      
Gross Amount Carried at close of period 12/31/2017, Land 9,700,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 81,552,129      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 91,252,129      
Accumulated Depreciation (36,965,435)      
Investment in Real Estate, Net 54,286,694      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Centre Club [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Ontario, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 412      
Initial Cost to Company, Land $ 7,436,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 33,014,789      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 8,651,651      
Gross Amount Carried at close of period 12/31/2017, Land 7,436,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 41,666,440      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 49,102,440      
Accumulated Depreciation (23,210,064)      
Investment in Real Estate, Net 25,892,376      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Church Corner [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Cambridge, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 85      
Initial Cost to Company, Land $ 5,220,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 16,744,643      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,757,280      
Gross Amount Carried at close of period 12/31/2017, Land 5,220,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 19,501,923      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 24,721,923      
Accumulated Depreciation (9,327,871)      
Investment in Real Estate, Net 15,394,052      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
City Gate at Cupertino (fka Cupertino) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Cupertino, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 311      
Initial Cost to Company, Land $ 40,400,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 95,937,046      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,063,652      
Gross Amount Carried at close of period 12/31/2017, Land 40,400,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 103,000,698      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 143,400,698      
Accumulated Depreciation (21,491,582)      
Investment in Real Estate, Net 121,909,116      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
City Pointe [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Fullerton, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 183      
Initial Cost to Company, Land $ 6,863,792      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 36,476,208      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,132,781      
Gross Amount Carried at close of period 12/31/2017, Land 6,863,792      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 37,608,989      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 44,472,781      
Accumulated Depreciation (12,911,899)      
Investment in Real Estate, Net 31,560,882      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
City Square Bellevue (fka Bellevue) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Bellevue, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 191      
Initial Cost to Company, Land $ 15,100,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 41,876,257      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,341,276      
Gross Amount Carried at close of period 12/31/2017, Land 15,100,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 45,217,533      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 60,317,533      
Accumulated Depreciation (9,816,078)      
Investment in Real Estate, Net 50,501,455      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
CityView at Longwood [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Boston, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 295      
Initial Cost to Company, Land $ 14,704,898      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 79,195,102      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 12,908,253      
Gross Amount Carried at close of period 12/31/2017, Land 14,704,898      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 92,103,355      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 106,808,253      
Accumulated Depreciation (29,583,293)      
Investment in Real Estate, Net 77,224,960      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Clarendon, The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 292      
Initial Cost to Company, Land $ 30,400,340      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 103,824,660      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,206,298      
Gross Amount Carried at close of period 12/31/2017, Land 30,400,340      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 106,030,958      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 136,431,298      
Accumulated Depreciation (30,102,780)      
Investment in Real Estate, Net 106,328,518      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Cleo, The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 92      
Initial Cost to Company, Land $ 6,615,467      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 14,829,335      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,872,824      
Gross Amount Carried at close of period 12/31/2017, Land 6,615,467      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 18,702,159      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 25,317,626      
Accumulated Depreciation (8,706,067)      
Investment in Real Estate, Net 16,611,559      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Connecticut Heights [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 518      
Initial Cost to Company, Land $ 27,600,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 114,002,295      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,582,335      
Gross Amount Carried at close of period 12/31/2017, Land 27,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 120,584,630      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 148,184,630      
Accumulated Depreciation (24,518,831)      
Investment in Real Estate, Net 123,665,799      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Corcoran House at DuPont Circle (fka DuPont Circle) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 138      
Initial Cost to Company, Land $ 13,500,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 26,913,113      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,863,273      
Gross Amount Carried at close of period 12/31/2017, Land 13,500,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 28,776,386      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 42,276,386      
Accumulated Depreciation (6,924,238)      
Investment in Real Estate, Net 35,352,148      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Courthouse Plaza [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 396      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 87,386,024      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,468,028      
Gross Amount Carried at close of period 12/31/2017, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 92,854,052      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 92,854,052      
Accumulated Depreciation (21,556,859)      
Investment in Real Estate, Net 71,297,193      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Creekside (San Mateo) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Mateo, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 192      
Initial Cost to Company, Land $ 9,606,600      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 21,193,231      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,232,377      
Gross Amount Carried at close of period 12/31/2017, Land 9,606,600      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 25,425,608      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 35,032,208      
Accumulated Depreciation (16,783,870)      
Investment in Real Estate, Net 18,248,338      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Cronins Landing [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Waltham, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 281      
Initial Cost to Company, Land $ 32,300,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 85,119,324      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,002,941      
Gross Amount Carried at close of period 12/31/2017, Land 32,300,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 91,122,265      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 123,422,265      
Accumulated Depreciation (19,414,857)      
Investment in Real Estate, Net 104,007,408      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Crystal Place [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 181      
Initial Cost to Company, Land $ 17,200,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 47,918,975      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,541,443      
Gross Amount Carried at close of period 12/31/2017, Land 17,200,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 51,460,418      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 68,660,418      
Accumulated Depreciation (11,376,670)      
Investment in Real Estate, Net 57,283,748      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Eagle Canyon [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Chino Hills, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 252      
Initial Cost to Company, Land $ 1,808,900      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 16,274,361      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 9,576,378      
Gross Amount Carried at close of period 12/31/2017, Land 1,808,900      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 25,850,739      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 27,659,639      
Accumulated Depreciation (18,419,631)      
Investment in Real Estate, Net 9,240,008      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Edgemont at Bethesda Metro [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Bethesda, MD      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 122      
Initial Cost to Company, Land $ 13,092,552      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 43,907,448      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,433,098      
Gross Amount Carried at close of period 12/31/2017, Land 13,092,552      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 45,340,546      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 58,433,098      
Accumulated Depreciation (11,970,483)      
Investment in Real Estate, Net 46,462,615      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Elevé [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Glendale, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 208      
Initial Cost to Company, Land $ 14,080,560      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 56,419,440      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 574,833      
Gross Amount Carried at close of period 12/31/2017, Land 14,080,560      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 56,994,273      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 71,074,833      
Accumulated Depreciation (9,935,529)      
Investment in Real Estate, Net 61,139,304      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Emerson Place [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Boston, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 444      
Initial Cost to Company, Land $ 14,855,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 57,566,636      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 27,713,125      
Gross Amount Carried at close of period 12/31/2017, Land 14,855,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 85,279,761      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 100,134,761      
Accumulated Depreciation (55,294,608)      
Investment in Real Estate, Net 44,840,153      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Encore at Sherman Oaks, The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Sherman Oaks, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 174      
Initial Cost to Company, Land $ 8,700,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 25,446,003      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,503,675      
Gross Amount Carried at close of period 12/31/2017, Land 8,700,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 26,949,678      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 35,649,678      
Accumulated Depreciation (8,805,442)      
Investment in Real Estate, Net 26,844,236      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Fountains at Emerald Park (fka Emerald Park) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Dublin, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 324      
Initial Cost to Company, Land $ 25,900,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 83,986,217      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,101,209      
Gross Amount Carried at close of period 12/31/2017, Land 25,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 85,087,426      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 110,987,426      
Accumulated Depreciation (18,972,556)      
Investment in Real Estate, Net 92,014,870      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Fremont Center [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Fremont, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 322      
Initial Cost to Company, Land $ 25,800,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 78,753,114      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,691,593      
Gross Amount Carried at close of period 12/31/2017, Land 25,800,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 82,444,707      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 108,244,707      
Accumulated Depreciation (18,108,606)      
Investment in Real Estate, Net 90,136,101      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Gallery, The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Hermosa Beach, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 169      
Initial Cost to Company, Land $ 18,144,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 46,567,941      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,765,229      
Gross Amount Carried at close of period 12/31/2017, Land 18,144,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 49,333,170      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 67,477,170      
Accumulated Depreciation (21,549,332)      
Investment in Real Estate, Net 45,927,838      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Garden Garage [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Boston, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 12,858,392      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2017, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 12,858,392      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 12,858,392      
Accumulated Depreciation 0      
Investment in Real Estate, Net 12,858,392      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Gateway at Malden Center [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Malden, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 203      
Initial Cost to Company, Land $ 9,209,780      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 25,722,666      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 14,271,535      
Gross Amount Carried at close of period 12/31/2017, Land 9,209,780      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 39,994,201      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 49,203,981      
Accumulated Depreciation (23,167,536)      
Investment in Real Estate, Net 26,036,445      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Geary Court Yard [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Francisco, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 164      
Initial Cost to Company, Land $ 1,722,400      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 15,471,429      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,981,389      
Gross Amount Carried at close of period 12/31/2017, Land 1,722,400      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 20,452,818      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 22,175,218      
Accumulated Depreciation (13,455,847)      
Investment in Real Estate, Net 8,719,371      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Hampshire Place [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 259      
Initial Cost to Company, Land $ 10,806,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 30,335,330      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,889,198      
Gross Amount Carried at close of period 12/31/2017, Land 10,806,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 36,224,528      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 47,030,528      
Accumulated Depreciation (16,825,383)      
Investment in Real Estate, Net 30,205,145      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Girard [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Boston, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 160      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 102,450,329      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 412,971      
Gross Amount Carried at close of period 12/31/2017, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 102,863,300      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 102,863,300      
Accumulated Depreciation (2,991,518)      
Investment in Real Estate, Net 99,871,782      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Harbor Steps [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 758      
Initial Cost to Company, Land $ 59,387,158      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 158,829,432      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 28,544,042      
Gross Amount Carried at close of period 12/31/2017, Land 59,387,158      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 187,373,474      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 246,760,632      
Accumulated Depreciation (80,511,164)      
Investment in Real Estate, Net 166,249,468      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Helios/1610 2nd Avenue [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 398      
Initial Cost to Company, Land $ 18,061,674      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 202,039,273      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2017, Land 18,061,674      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 202,039,273      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 220,100,947      
Accumulated Depreciation (3,845,290)      
Investment in Real Estate, Net 216,255,657      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Heritage at Stone Ridge [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Burlington, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 180      
Initial Cost to Company, Land $ 10,800,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 31,808,335      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,313,536      
Gross Amount Carried at close of period 12/31/2017, Land 10,800,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 34,121,871      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 44,921,871      
Accumulated Depreciation (15,330,866)      
Investment in Real Estate, Net 29,591,005      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Heritage Ridge [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Lynwood, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 197      
Initial Cost to Company, Land $ 6,895,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 18,983,597      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,339,062      
Gross Amount Carried at close of period 12/31/2017, Land 6,895,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 22,322,659      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 29,217,659      
Accumulated Depreciation (10,066,945)      
Investment in Real Estate, Net 19,150,714      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Hesby [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location North Hollywood, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 308      
Initial Cost to Company, Land $ 23,299,892      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 102,700,108      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 575,827      
Gross Amount Carried at close of period 12/31/2017, Land 23,299,892      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 103,275,935      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 126,575,827      
Accumulated Depreciation (17,235,969)      
Investment in Real Estate, Net 109,339,858      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Highlands At South Plainfield [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location South Plainfield, NJ      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 252      
Initial Cost to Company, Land $ 10,080,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 37,526,912      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,968,410      
Gross Amount Carried at close of period 12/31/2017, Land 10,080,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 39,495,322      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 49,575,322      
Accumulated Depreciation (17,281,612)      
Investment in Real Estate, Net 32,293,710      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Hikari [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 128      
Initial Cost to Company, Land $ 9,435,760      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 32,564,240      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 813,913      
Gross Amount Carried at close of period 12/31/2017, Land 9,435,760      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 33,378,153      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 42,813,913      
Accumulated Depreciation (9,383,982)      
Investment in Real Estate, Net 33,429,931      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Hudson Crossing [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 259      
Initial Cost to Company, Land $ 23,420,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 69,977,699      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,333,449      
Gross Amount Carried at close of period 12/31/2017, Land 23,420,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 72,311,148      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 95,731,148      
Accumulated Depreciation (33,463,902)      
Investment in Real Estate, Net 62,267,246      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Hudson Pointe [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Jersey City, NJ      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 182      
Initial Cost to Company, Land $ 5,350,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 41,114,074      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,026,931      
Gross Amount Carried at close of period 12/31/2017, Land 5,350,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 47,141,005      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 52,491,005      
Accumulated Depreciation (22,111,343)      
Investment in Real Estate, Net 30,379,662      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Hunt Club II [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Charlotte, NC      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 100,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 0      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2017, Land 100,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 100,000      
Accumulated Depreciation 0      
Investment in Real Estate, Net 100,000      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Ivory Wood [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Bothell, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 144      
Initial Cost to Company, Land $ 2,732,800      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 13,888,282      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,259,914      
Gross Amount Carried at close of period 12/31/2017, Land 2,732,800      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 15,148,196      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 17,880,996      
Accumulated Depreciation (7,400,504)      
Investment in Real Estate, Net 10,480,492      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Jia [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 280      
Initial Cost to Company, Land $ 14,791,831      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 77,426,315      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 281,313      
Gross Amount Carried at close of period 12/31/2017, Land 14,791,831      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 77,707,628      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 92,499,459      
Accumulated Depreciation (15,513,371)      
Investment in Real Estate, Net 76,986,088      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Junction 47 (fka West Seattle) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 206      
Initial Cost to Company, Land $ 11,726,305      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 56,108,989      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 36,260      
Gross Amount Carried at close of period 12/31/2017, Land 11,726,305      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 56,145,249      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 67,871,554      
Accumulated Depreciation (5,156,854)      
Investment in Real Estate, Net 62,714,700      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Kelvin, The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Irvine, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 194      
Initial Cost to Company, Land $ 15,521,552      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 64,853,448      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 385,466      
Gross Amount Carried at close of period 12/31/2017, Land 15,521,552      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 65,238,914      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 80,760,466      
Accumulated Depreciation (7,677,409)      
Investment in Real Estate, Net 73,083,057      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Landings at Port Imperial [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location W. New York, NJ      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 276      
Initial Cost to Company, Land $ 27,246,045      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 37,741,050      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 10,790,636      
Gross Amount Carried at close of period 12/31/2017, Land 27,246,045      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 48,531,686      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 75,777,731      
Accumulated Depreciation (29,235,083)      
Investment in Real Estate, Net 46,542,648      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Lincoln Heights [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Quincy, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 336      
Initial Cost to Company, Land $ 5,928,400      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 33,595,262      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 13,797,904      
Gross Amount Carried at close of period 12/31/2017, Land 5,928,400      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 47,393,166      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 53,321,566      
Accumulated Depreciation (34,170,500)      
Investment in Real Estate, Net 19,151,066      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Lindley Apartments [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Encino, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 129      
Initial Cost to Company, Land $ 5,805,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 25,705,000      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,086,410      
Gross Amount Carried at close of period 12/31/2017, Land 5,805,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 26,791,410      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 32,596,410      
Accumulated Depreciation (8,393,740)      
Investment in Real Estate, Net 24,202,670      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Loft 590 [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 212      
Initial Cost to Company, Land $ 20,100,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 67,909,023      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 688,579      
Gross Amount Carried at close of period 12/31/2017, Land 20,100,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 68,597,602      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 88,697,602      
Accumulated Depreciation (13,789,656)      
Investment in Real Estate, Net 74,907,946      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Lofts at Kendall Square (fka Kendall Square) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Cambridge, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 186      
Initial Cost to Company, Land $ 18,696,674      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 78,445,657      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,737,350      
Gross Amount Carried at close of period 12/31/2017, Land 18,696,674      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 84,183,007      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 102,879,681      
Accumulated Depreciation (17,496,435)      
Investment in Real Estate, Net 85,383,246      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Longacre House [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 293      
Initial Cost to Company, Land $ 73,170,045      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 53,962,510      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,572,439      
Gross Amount Carried at close of period 12/31/2017, Land 73,170,045      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 56,534,949      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 129,704,994      
Accumulated Depreciation (22,561,960)      
Investment in Real Estate, Net 107,143,034      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Longfellow Place [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Boston, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 710      
Initial Cost to Company, Land $ 47,096,917      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 150,143,916      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 86,838,642      
Gross Amount Carried at close of period 12/31/2017, Land 47,096,917      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 236,982,558      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 284,079,475      
Accumulated Depreciation (154,305,979)      
Investment in Real Estate, Net 129,773,496      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Mantena [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 98      
Initial Cost to Company, Land $ 22,346,513      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 61,501,158      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 813,638      
Gross Amount Carried at close of period 12/31/2017, Land 22,346,513      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 62,314,796      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 84,661,309      
Accumulated Depreciation (13,828,043)      
Investment in Real Estate, Net 70,833,266      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Marina 41 (fka Marina Del Rey) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Marina Del Rey, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 623      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 168,842,442      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,492,153      
Gross Amount Carried at close of period 12/31/2017, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 175,334,595      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 175,334,595      
Accumulated Depreciation (40,843,073)      
Investment in Real Estate, Net 134,491,522      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Mariposa at Playa Del Rey (fka Playa Del Rey) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Playa Del Rey, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 354      
Initial Cost to Company, Land $ 60,900,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 89,311,482      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,201,127      
Gross Amount Carried at close of period 12/31/2017, Land 60,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 94,512,609      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 155,412,609      
Accumulated Depreciation (21,025,902)      
Investment in Real Estate, Net 134,386,707      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Milano Lofts [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 99      
Initial Cost to Company, Land $ 8,125,216      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 27,378,784      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,088,041      
Gross Amount Carried at close of period 12/31/2017, Land 8,125,216      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 28,466,825      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 36,592,041      
Accumulated Depreciation (6,979,083)      
Investment in Real Estate, Net 29,612,958      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Mosaic at Metro [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Hyattsville, MD      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 260      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 59,580,898      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 955,743      
Gross Amount Carried at close of period 12/31/2017, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 60,536,641      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 60,536,641      
Accumulated Depreciation (19,462,344)      
Investment in Real Estate, Net 41,074,297      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Mountain View Redevelopment [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Mountain View, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 17,876      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2017, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 17,876      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 17,876      
Accumulated Depreciation 0      
Investment in Real Estate, Net 17,876      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Mozaic at Union Station [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 272      
Initial Cost to Company, Land $ 8,500,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 52,529,446      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,126,281      
Gross Amount Carried at close of period 12/31/2017, Land 8,500,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 54,655,727      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 63,155,727      
Accumulated Depreciation (22,181,465)      
Investment in Real Estate, Net 40,974,262      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Murray Hill Tower (fka Murray Hill) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 270      
Initial Cost to Company, Land $ 75,800,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 102,705,401      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 8,886,567      
Gross Amount Carried at close of period 12/31/2017, Land 75,800,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 111,591,968      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 187,391,968      
Accumulated Depreciation (25,690,086)      
Investment in Real Estate, Net 161,701,882      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
North Pier at Harborside [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Jersey City, NJ      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 297      
Initial Cost to Company, Land $ 4,000,159      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 94,290,590      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,047,215      
Gross Amount Carried at close of period 12/31/2017, Land 4,000,159      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 98,337,805      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 102,337,964      
Accumulated Depreciation (46,111,052)      
Investment in Real Estate, Net 56,226,912      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Northglen [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Valencia, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 234      
Initial Cost to Company, Land $ 9,360,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 20,778,553      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,506,094      
Gross Amount Carried at close of period 12/31/2017, Land 9,360,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 25,284,647      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 34,644,647      
Accumulated Depreciation (14,197,899)      
Investment in Real Estate, Net 20,446,748      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Northpark [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Burlingame, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 510      
Initial Cost to Company, Land $ 38,607,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 77,472,217      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 13,899,131      
Gross Amount Carried at close of period 12/31/2017, Land 38,607,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 91,371,348      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 129,978,348      
Accumulated Depreciation (32,707,629)      
Investment in Real Estate, Net 97,270,719      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Northridge [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Pleasant Hill, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 221      
Initial Cost to Company, Land $ 5,524,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 14,691,705      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 10,828,364      
Gross Amount Carried at close of period 12/31/2017, Land 5,524,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 25,520,069      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 31,044,069      
Accumulated Depreciation (18,623,618)      
Investment in Real Estate, Net 12,420,451      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Oak Park Combined [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Agoura Hills, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 444      
Initial Cost to Company, Land $ 3,390,700      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 30,517,274      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 10,331,701      
Gross Amount Carried at close of period 12/31/2017, Land 3,390,700      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 40,848,975      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 44,239,675      
Accumulated Depreciation (30,282,737)      
Investment in Real Estate, Net 13,956,938      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Oakwood Boston [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Boston, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 94      
Initial Cost to Company, Land $ 22,200,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 28,672,979      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,616,791      
Gross Amount Carried at close of period 12/31/2017, Land 22,200,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 30,289,770      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 52,489,770      
Accumulated Depreciation (7,037,665)      
Investment in Real Estate, Net 45,452,105      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Oakwood Crystal City [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 162      
Initial Cost to Company, Land $ 15,400,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 35,474,336      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,757,149      
Gross Amount Carried at close of period 12/31/2017, Land 15,400,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 39,231,485      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 54,631,485      
Accumulated Depreciation (8,406,119)      
Investment in Real Estate, Net 46,225,366      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Oakwood Marina Del Rey [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Marina Del Rey, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 597      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 120,795,359      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,723,823      
Gross Amount Carried at close of period 12/31/2017, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 123,519,182      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 123,519,182      
Accumulated Depreciation (29,036,612)      
Investment in Real Estate, Net 94,482,570      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Oaks [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Santa Clarita, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 520      
Initial Cost to Company, Land $ 23,400,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 61,020,438      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,585,786      
Gross Amount Carried at close of period 12/31/2017, Land 23,400,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 66,606,224      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 90,006,224      
Accumulated Depreciation (34,133,995)      
Investment in Real Estate, Net 55,872,229      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Ocean Crest [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Solana Beach, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 146      
Initial Cost to Company, Land $ 5,111,200      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 11,910,438      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,250,627      
Gross Amount Carried at close of period 12/31/2017, Land 5,111,200      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 16,161,065      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 21,272,265      
Accumulated Depreciation (10,492,882)      
Investment in Real Estate, Net 10,779,383      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Odin (fka Tallman) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 301      
Initial Cost to Company, Land $ 16,807,519      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 63,645,480      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 9,233      
Gross Amount Carried at close of period 12/31/2017, Land 16,807,519      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 63,654,713      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 80,462,232      
Accumulated Depreciation (5,819,185)      
Investment in Real Estate, Net 74,643,047      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Old Town Lofts [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Redmond, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 149      
Initial Cost to Company, Land $ 7,740,467      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 44,146,181      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 784,750      
Gross Amount Carried at close of period 12/31/2017, Land 7,740,467      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 44,930,931      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 52,671,398      
Accumulated Depreciation (5,125,092)      
Investment in Real Estate, Net 47,546,306      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
One Henry Adams [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Francisco, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 241      
Initial Cost to Company, Land $ 30,224,393      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 137,031,168      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,724      
Gross Amount Carried at close of period 12/31/2017, Land 30,224,393      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 137,037,892      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 167,262,285      
Accumulated Depreciation (5,417,321)      
Investment in Real Estate, Net 161,844,964      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Pacific Place [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 430      
Initial Cost to Company, Land $ 32,250,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 110,750,000      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,483,644      
Gross Amount Carried at close of period 12/31/2017, Land 32,250,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 112,233,644      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 144,483,644      
Accumulated Depreciation (23,253,190)      
Investment in Real Estate, Net 121,230,454      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Packard Building [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 61      
Initial Cost to Company, Land $ 5,911,041      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 19,954,959      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 226,050      
Gross Amount Carried at close of period 12/31/2017, Land 5,911,041      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 20,181,009      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 26,092,050      
Accumulated Depreciation (2,148,366)      
Investment in Real Estate, Net 23,943,684      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Parc 77 [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 137      
Initial Cost to Company, Land $ 40,504,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 18,025,679      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,041,700      
Gross Amount Carried at close of period 12/31/2017, Land 40,504,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 24,067,379      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 64,571,379      
Accumulated Depreciation (12,290,428)      
Investment in Real Estate, Net 52,280,951      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Parc Cameron [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 166      
Initial Cost to Company, Land $ 37,600,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 9,855,597      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,300,028      
Gross Amount Carried at close of period 12/31/2017, Land 37,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 17,155,625      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 54,755,625      
Accumulated Depreciation (10,340,621)      
Investment in Real Estate, Net 44,415,004      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Parc Coliseum [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 177      
Initial Cost to Company, Land $ 52,654,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 23,045,751      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 8,978,751      
Gross Amount Carried at close of period 12/31/2017, Land 52,654,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 32,024,502      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 84,678,502      
Accumulated Depreciation (16,948,295)      
Investment in Real Estate, Net 67,730,207      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Parc East Towers [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 324      
Initial Cost to Company, Land $ 102,163,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 108,989,402      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 10,236,255      
Gross Amount Carried at close of period 12/31/2017, Land 102,163,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 119,225,657      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 221,388,657      
Accumulated Depreciation (48,273,891)      
Investment in Real Estate, Net 173,114,766      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Parc on Powell (fka Parkside at Emeryville) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Emeryville, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 173      
Initial Cost to Company, Land $ 16,667,059      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 65,071,885      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 224,676      
Gross Amount Carried at close of period 12/31/2017, Land 16,667,059      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 65,296,561      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 81,963,620      
Accumulated Depreciation (6,675,129)      
Investment in Real Estate, Net 75,288,491      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Park at Pentagon Row (fka Pentagon City) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 298      
Initial Cost to Company, Land $ 28,300,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 78,838,184      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,995,147      
Gross Amount Carried at close of period 12/31/2017, Land 28,300,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 80,833,331      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 109,133,331      
Accumulated Depreciation (17,268,528)      
Investment in Real Estate, Net 91,864,803      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Park Connecticut [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 142      
Initial Cost to Company, Land $ 13,700,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 59,087,519      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,447,815      
Gross Amount Carried at close of period 12/31/2017, Land 13,700,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 60,535,334      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 74,235,334      
Accumulated Depreciation (12,311,907)      
Investment in Real Estate, Net 61,923,427      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Park Hacienda (fka Hacienda) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Pleasanton, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 540      
Initial Cost to Company, Land $ 43,200,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 128,753,359      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,520,251      
Gross Amount Carried at close of period 12/31/2017, Land 43,200,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 131,273,610      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 174,473,610      
Accumulated Depreciation (29,930,085)      
Investment in Real Estate, Net 144,543,525      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Park West (CA) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 444      
Initial Cost to Company, Land $ 3,033,500      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 27,302,383      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 10,420,073      
Gross Amount Carried at close of period 12/31/2017, Land 3,033,500      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 37,722,456      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 40,755,956      
Accumulated Depreciation (27,786,714)      
Investment in Real Estate, Net 12,969,242      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Parkside [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Union City, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 208      
Initial Cost to Company, Land $ 6,246,700      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 11,827,453      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,452,846      
Gross Amount Carried at close of period 12/31/2017, Land 6,246,700      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 17,280,299      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 23,526,999      
Accumulated Depreciation (11,589,006)      
Investment in Real Estate, Net 11,937,993      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Pearl, The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 80      
Initial Cost to Company, Land $ 6,972,585      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 26,527,415      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 556,995      
Gross Amount Carried at close of period 12/31/2017, Land 6,972,585      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 27,084,410      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 34,056,995      
Accumulated Depreciation (2,841,186)      
Investment in Real Estate, Net 31,215,809      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Pegasus [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 322      
Initial Cost to Company, Land $ 18,094,052      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 81,905,948      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,943,360      
Gross Amount Carried at close of period 12/31/2017, Land 18,094,052      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 86,849,308      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 104,943,360      
Accumulated Depreciation (26,155,411)      
Investment in Real Estate, Net 78,787,949      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Playa Pacifica [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Hermosa Beach, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 285      
Initial Cost to Company, Land $ 35,100,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 33,473,822      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 22,912,647      
Gross Amount Carried at close of period 12/31/2017, Land 35,100,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 56,386,469      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 91,486,469      
Accumulated Depreciation (25,547,975)      
Investment in Real Estate, Net 65,938,494      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Portofino [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Chino Hills, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 176      
Initial Cost to Company, Land $ 3,572,400      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 14,660,994      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,713,205      
Gross Amount Carried at close of period 12/31/2017, Land 3,572,400      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 18,374,199      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 21,946,599      
Accumulated Depreciation (12,779,600)      
Investment in Real Estate, Net 9,166,999      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Portofino (Val) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Valencia, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 216      
Initial Cost to Company, Land $ 8,640,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 21,487,126      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,380,999      
Gross Amount Carried at close of period 12/31/2017, Land 8,640,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 26,868,125      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 35,508,125      
Accumulated Depreciation (15,359,183)      
Investment in Real Estate, Net 20,148,942      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Portside Towers [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Jersey City, NJ      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 527      
Initial Cost to Company, Land $ 22,487,006      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 96,842,913      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 21,767,146      
Gross Amount Carried at close of period 12/31/2017, Land 22,487,006      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 118,610,059      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 141,097,065      
Accumulated Depreciation (80,249,602)      
Investment in Real Estate, Net 60,847,463      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Potrero 1010 [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Francisco, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 453      
Initial Cost to Company, Land $ 40,830,011      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 178,932,843      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 16,775      
Gross Amount Carried at close of period 12/31/2017, Land 40,830,011      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 178,949,618      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 219,779,629      
Accumulated Depreciation (11,563,892)      
Investment in Real Estate, Net 208,215,737      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Prado (fka Glendale) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Glendale, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 264      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 67,977,313      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,211,660      
Gross Amount Carried at close of period 12/31/2017, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 71,188,973      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 71,188,973      
Accumulated Depreciation (15,429,230)      
Investment in Real Estate, Net 55,759,743      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Prime, The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 256      
Initial Cost to Company, Land $ 32,000,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 64,436,539      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,417,186      
Gross Amount Carried at close of period 12/31/2017, Land 32,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 65,853,725      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 97,853,725      
Accumulated Depreciation (27,697,067)      
Investment in Real Estate, Net 70,156,658      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Prism at Park Avenue South (fka 400 Park Aveue South (EQR)) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 269      
Initial Cost to Company, Land $ 76,292,169      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 172,553,723      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 90,272      
Gross Amount Carried at close of period 12/31/2017, Land 76,292,169      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 172,643,995      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 248,936,164      
Accumulated Depreciation (18,802,832)      
Investment in Real Estate, Net 230,133,332      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Promenade at Town Center I & II [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Valencia, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 564      
Initial Cost to Company, Land $ 28,200,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 69,795,915      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 8,077,724      
Gross Amount Carried at close of period 12/31/2017, Land 28,200,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 77,873,639      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 106,073,639      
Accumulated Depreciation (38,490,478)      
Investment in Real Estate, Net 67,583,161      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Quarry Hills [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Quincy, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 316      
Initial Cost to Company, Land $ 26,900,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 84,411,162      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,089,632      
Gross Amount Carried at close of period 12/31/2017, Land 26,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 86,500,794      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 113,400,794      
Accumulated Depreciation (19,076,341)      
Investment in Real Estate, Net 94,324,453      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Providence [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Bothell, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 200      
Initial Cost to Company, Land $ 3,573,621      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 19,055,505      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,051,612      
Gross Amount Carried at close of period 12/31/2017, Land 3,573,621      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 21,107,117      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 24,680,738      
Accumulated Depreciation (10,234,226)      
Investment in Real Estate, Net 14,446,512      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Red 160 (fka Redmond Way) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Redmond, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 250      
Initial Cost to Company, Land $ 15,546,376      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 65,320,010      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,166,488      
Gross Amount Carried at close of period 12/31/2017, Land 15,546,376      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 66,486,498      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 82,032,874      
Accumulated Depreciation (16,019,260)      
Investment in Real Estate, Net 66,013,614      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Redmond Court [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Bellevue, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 206      
Initial Cost to Company, Land $ 10,300,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 33,488,745      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 900,433      
Gross Amount Carried at close of period 12/31/2017, Land 10,300,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 34,389,178      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 44,689,178      
Accumulated Depreciation (8,390,947)      
Investment in Real Estate, Net 36,298,231      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Radius Koreatown [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 301      
Initial Cost to Company, Land $ 32,494,154      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 84,645,202      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 22,940      
Gross Amount Carried at close of period 12/31/2017, Land 32,494,154      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 84,668,142      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 117,162,296      
Accumulated Depreciation (2,949,192)      
Investment in Real Estate, Net 114,213,104      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Regency Palms [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Huntington Beach, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 310      
Initial Cost to Company, Land $ 1,857,400      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 16,713,254      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,014,242      
Gross Amount Carried at close of period 12/31/2017, Land 1,857,400      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 22,727,496      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 24,584,896      
Accumulated Depreciation (17,510,000)      
Investment in Real Estate, Net 7,074,896      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Renaissance Villas [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Berkeley, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 34      
Initial Cost to Company, Land $ 2,458,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 4,542,000      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 184,192      
Gross Amount Carried at close of period 12/31/2017, Land 2,458,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 4,726,192      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 7,184,192      
Accumulated Depreciation (1,859,882)      
Investment in Real Estate, Net 5,324,310      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Reserve at Mountain View (fka Mountain View) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Mountain View, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 180      
Initial Cost to Company, Land $ 27,000,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 33,029,605      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,606,368      
Gross Amount Carried at close of period 12/31/2017, Land 27,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 39,635,973      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 66,635,973      
Accumulated Depreciation (8,901,550)      
Investment in Real Estate, Net 57,734,423      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Reserve at Potomac Yard [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Alexandria, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 588      
Initial Cost to Company, Land $ 11,918,917      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 68,862,641      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 13,703,091      
Gross Amount Carried at close of period 12/31/2017, Land 11,918,917      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 82,565,732      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 94,484,649      
Accumulated Depreciation (38,310,647)      
Investment in Real Estate, Net 56,174,002      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Reserve at Town Center I-III (WA) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Mill Creek, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 584      
Initial Cost to Company, Land $ 16,768,705      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 77,511,523      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,631,274      
Gross Amount Carried at close of period 12/31/2017, Land 16,768,705      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 81,142,797      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 97,911,502      
Accumulated Depreciation (30,389,852)      
Investment in Real Estate, Net 67,521,650      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Reserve at Empire Lakes [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Rancho Cucamonga, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 467      
Initial Cost to Company, Land $ 16,345,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 73,080,670      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,031,630      
Gross Amount Carried at close of period 12/31/2017, Land 16,345,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 76,112,300      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 92,457,300      
Accumulated Depreciation (33,721,496)      
Investment in Real Estate, Net 58,735,804      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Residences at Westgate I (fka Westage II) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Pasadena, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 252      
Initial Cost to Company, Land $ 17,859,785      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 109,033,369      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 244,721      
Gross Amount Carried at close of period 12/31/2017, Land 17,859,785      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 109,278,090      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 127,137,875      
Accumulated Depreciation (16,997,966)      
Investment in Real Estate, Net 110,139,909      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Residences at Westgate II (fka Westgage III) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Pasadena, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 88      
Initial Cost to Company, Land $ 12,118,248      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 40,420,828      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 50,108      
Gross Amount Carried at close of period 12/31/2017, Land 12,118,248      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 40,470,936      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 52,589,184      
Accumulated Depreciation (4,259,073)      
Investment in Real Estate, Net 48,330,111      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Rianna I [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 78      
Initial Cost to Company, Land $ 2,268,160      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 14,864,482      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 594,152      
Gross Amount Carried at close of period 12/31/2017, Land 2,268,160      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 15,458,634      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 17,726,794      
Accumulated Depreciation (5,412,019)      
Investment in Real Estate, Net 12,314,775      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Ridgewood Village I&II [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Diego, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 408      
Initial Cost to Company, Land $ 11,809,500      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 34,004,048      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,628,651      
Gross Amount Carried at close of period 12/31/2017, Land 11,809,500      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 39,632,699      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 51,442,199      
Accumulated Depreciation (24,659,415)      
Investment in Real Estate, Net 26,782,784      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Riva Terra I (fka Redwood Shores) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Redwood City, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 304      
Initial Cost to Company, Land $ 34,963,355      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 84,587,658      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,238,246      
Gross Amount Carried at close of period 12/31/2017, Land 34,963,355      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 87,825,904      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 122,789,259      
Accumulated Depreciation (20,223,427)      
Investment in Real Estate, Net 102,565,832      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Riva Terra II (fka Harborside) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Redwood City, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 149      
Initial Cost to Company, Land $ 17,136,645      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 40,536,531      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,064,253      
Gross Amount Carried at close of period 12/31/2017, Land 17,136,645      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 42,600,784      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 59,737,429      
Accumulated Depreciation (9,084,137)      
Investment in Real Estate, Net 50,653,292      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Riverpark [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Redmond, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 321      
Initial Cost to Company, Land $ 14,355,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 80,894,049      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,514,535      
Gross Amount Carried at close of period 12/31/2017, Land 14,355,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 84,408,584      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 98,763,584      
Accumulated Depreciation (21,590,814)      
Investment in Real Estate, Net 77,172,770      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Rianna II [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 78      
Initial Cost to Company, Land $ 2,161,840      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 14,433,614      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 387,624      
Gross Amount Carried at close of period 12/31/2017, Land 2,161,840      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 14,821,238      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 16,983,078      
Accumulated Depreciation (5,134,291)      
Investment in Real Estate, Net 11,848,787      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Rosecliff II [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Quincy, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 130      
Initial Cost to Company, Land $ 4,922,840      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 30,202,160      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,107,943      
Gross Amount Carried at close of period 12/31/2017, Land 4,922,840      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 31,310,103      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 36,232,943      
Accumulated Depreciation (9,015,949)      
Investment in Real Estate, Net 27,216,994      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Sakura Crossing [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 230      
Initial Cost to Company, Land $ 14,641,990      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 42,858,010      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 945,394      
Gross Amount Carried at close of period 12/31/2017, Land 14,641,990      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 43,803,404      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 58,445,394      
Accumulated Depreciation (13,215,641)      
Investment in Real Estate, Net 45,229,753      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Seventh & James [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 96      
Initial Cost to Company, Land $ 663,800      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 5,974,803      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,891,414      
Gross Amount Carried at close of period 12/31/2017, Land 663,800      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 9,866,217      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 10,530,017      
Accumulated Depreciation (7,394,440)      
Investment in Real Estate, Net 3,135,577      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Sheffield Court [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 597      
Initial Cost to Company, Land $ 3,342,381      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 31,337,332      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 14,580,051      
Gross Amount Carried at close of period 12/31/2017, Land 3,342,381      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 45,917,383      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 49,259,764      
Accumulated Depreciation (35,827,987)      
Investment in Real Estate, Net 13,431,777      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Skycrest [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Valencia, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 264      
Initial Cost to Company, Land $ 10,560,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 25,574,457      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,456,198      
Gross Amount Carried at close of period 12/31/2017, Land 10,560,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 30,030,655      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 40,590,655      
Accumulated Depreciation (17,139,075)      
Investment in Real Estate, Net 23,451,580      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Skylark [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Union City, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 174      
Initial Cost to Company, Land $ 1,781,600      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 16,731,916      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,392,507      
Gross Amount Carried at close of period 12/31/2017, Land 1,781,600      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 22,124,423      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 23,906,023      
Accumulated Depreciation (13,428,913)      
Investment in Real Estate, Net 10,477,110      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Skyline Terrace [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Burlingame, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 138      
Initial Cost to Company, Land $ 16,836,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 35,414,000      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,163,764      
Gross Amount Carried at close of period 12/31/2017, Land 16,836,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 40,577,764      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 57,413,764      
Accumulated Depreciation (13,281,197)      
Investment in Real Estate, Net 44,132,567      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Skyline Towers [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Falls Church, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 939      
Initial Cost to Company, Land $ 78,278,200      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 91,485,591      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 43,209,046      
Gross Amount Carried at close of period 12/31/2017, Land 78,278,200      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 134,694,637      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 212,972,837      
Accumulated Depreciation (72,629,553)      
Investment in Real Estate, Net 140,343,284      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
SoMa II [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Francisco, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 29,406,606      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 5,393,139      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2017, Land 29,406,606      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 5,393,139      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 34,799,745      
Accumulated Depreciation 0      
Investment in Real Estate, Net 34,799,745      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Sonterra at Foothill Ranch [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Foothill Ranch, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 300      
Initial Cost to Company, Land $ 7,503,400      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 24,048,507      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,811,134      
Gross Amount Carried at close of period 12/31/2017, Land 7,503,400      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 29,859,641      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 37,363,041      
Accumulated Depreciation (18,657,410)      
Investment in Real Estate, Net 18,705,631      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
South City Station (fka South San Francisco) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Francisco, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 360      
Initial Cost to Company, Land $ 68,900,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 79,476,861      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,784,286      
Gross Amount Carried at close of period 12/31/2017, Land 68,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 82,261,147      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 151,161,147      
Accumulated Depreciation (18,547,168)      
Investment in Real Estate, Net 132,613,979      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Southwood [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Palo Alto, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 100      
Initial Cost to Company, Land $ 6,936,600      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 14,324,069      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,215,343      
Gross Amount Carried at close of period 12/31/2017, Land 6,936,600      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 18,539,412      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 25,476,012      
Accumulated Depreciation (12,007,752)      
Investment in Real Estate, Net 13,468,260      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Springbrook Estates [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Riverside, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 18,200,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 0      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2017, Land 18,200,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 18,200,000      
Accumulated Depreciation 0      
Investment in Real Estate, Net 18,200,000      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Summerset Village II [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Chatsworth, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 260,646      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 0      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2017, Land 260,646      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 260,646      
Accumulated Depreciation 0      
Investment in Real Estate, Net 260,646      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Summit at Sausalito (fka Sausalito) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Sausalito, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 198      
Initial Cost to Company, Land $ 26,000,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 28,435,024      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,286,153      
Gross Amount Carried at close of period 12/31/2017, Land 26,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 34,721,177      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 60,721,177      
Accumulated Depreciation (9,412,796)      
Investment in Real Estate, Net 51,308,381      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Springline [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 136      
Initial Cost to Company, Land $ 9,163,666      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 47,910,981      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 149,570      
Gross Amount Carried at close of period 12/31/2017, Land 9,163,666      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 48,060,551      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 57,224,217      
Accumulated Depreciation (2,733,027)      
Investment in Real Estate, Net 54,491,190      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Ten23 (fka 500 West 23rd Street) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 111      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 58,881,873      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 200,907      
Gross Amount Carried at close of period 12/31/2017, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 59,082,780      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 59,082,780      
Accumulated Depreciation (12,278,031)      
Investment in Real Estate, Net 46,804,749      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Town Square at Mark Center II [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Alexandria, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 272      
Initial Cost to Company, Land $ 15,568,464      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 55,029,607      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,744,364      
Gross Amount Carried at close of period 12/31/2017, Land 15,568,464      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 58,773,971      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 74,342,435      
Accumulated Depreciation (19,047,027)      
Investment in Real Estate, Net 55,295,408      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Terraces, The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Francisco, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 117      
Initial Cost to Company, Land $ 14,087,610      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 16,314,151      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,262,327      
Gross Amount Carried at close of period 12/31/2017, Land 14,087,610      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 17,576,478      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 31,664,088      
Accumulated Depreciation (5,789,387)      
Investment in Real Estate, Net 25,874,701      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Urbana (fka Market Street Landing) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 287      
Initial Cost to Company, Land $ 12,542,418      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 75,766,505      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 346,564      
Gross Amount Carried at close of period 12/31/2017, Land 12,542,418      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 76,113,069      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 88,655,487      
Accumulated Depreciation (14,010,017)      
Investment in Real Estate, Net 74,645,470      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Third Square [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Cambridge, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 471      
Initial Cost to Company, Land $ 26,767,171      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 218,822,728      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,733,059      
Gross Amount Carried at close of period 12/31/2017, Land 26,767,171      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 225,555,787      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 252,322,958      
Accumulated Depreciation (70,108,714)      
Investment in Real Estate, Net 182,214,244      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Uwajimaya Village [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 176      
Initial Cost to Company, Land $ 8,800,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 22,188,288      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,728,090      
Gross Amount Carried at close of period 12/31/2017, Land 8,800,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 23,916,378      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 32,716,378      
Accumulated Depreciation (10,901,158)      
Investment in Real Estate, Net 21,815,220      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Three20 [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 134      
Initial Cost to Company, Land $ 7,030,766      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 29,005,762      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 729,045      
Gross Amount Carried at close of period 12/31/2017, Land 7,030,766      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 29,734,807      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 36,765,573      
Accumulated Depreciation (5,577,508)      
Investment in Real Estate, Net 31,188,065      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Vantage Pointe [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Diego, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 679      
Initial Cost to Company, Land $ 9,403,960      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 190,596,040      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 9,156,867      
Gross Amount Carried at close of period 12/31/2017, Land 9,403,960      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 199,752,907      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 209,156,867      
Accumulated Depreciation (59,435,552)      
Investment in Real Estate, Net 149,721,315      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Town Center South Commercial [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location St. Charles, MD      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 1,500,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 9,394      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2017, Land 1,500,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 9,394      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 1,509,394      
Accumulated Depreciation 0      
Investment in Real Estate, Net 1,509,394      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Veloce [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Redmond, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 322      
Initial Cost to Company, Land $ 15,322,724      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 76,176,594      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,246,516      
Gross Amount Carried at close of period 12/31/2017, Land 15,322,724      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 77,423,110      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 92,745,834      
Accumulated Depreciation (17,729,126)      
Investment in Real Estate, Net 75,016,708      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Verde Condominium Homes (fka Mission Verde, LLC) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Jose, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 108      
Initial Cost to Company, Land $ 5,190,700      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 9,679,109      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,309,244      
Gross Amount Carried at close of period 12/31/2017, Land 5,190,700      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 13,988,353      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 19,179,053      
Accumulated Depreciation (9,877,543)      
Investment in Real Estate, Net 9,301,510      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Veridian (fka Silver Spring) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Silver Spring, MD      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 457      
Initial Cost to Company, Land $ 18,539,817      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 130,407,365      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,078,639      
Gross Amount Carried at close of period 12/31/2017, Land 18,539,817      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 133,486,004      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 152,025,821      
Accumulated Depreciation (39,137,932)      
Investment in Real Estate, Net 112,887,889      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Villa Solana [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Laguna Hills, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 272      
Initial Cost to Company, Land $ 1,665,100      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 14,985,678      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 9,752,842      
Gross Amount Carried at close of period 12/31/2017, Land 1,665,100      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 24,738,520      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 26,403,620      
Accumulated Depreciation (19,582,595)      
Investment in Real Estate, Net 6,821,025      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Village at Del Mar Heights, The (fka Del Mar Heights) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Diego, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 168      
Initial Cost to Company, Land $ 15,100,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 40,859,396      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,315,901      
Gross Amount Carried at close of period 12/31/2017, Land 15,100,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 42,175,297      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 57,275,297      
Accumulated Depreciation (9,628,990)      
Investment in Real Estate, Net 47,646,307      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Virginia Square [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 231      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 85,940,003      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,594,826      
Gross Amount Carried at close of period 12/31/2017, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 90,534,829      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 90,534,829      
Accumulated Depreciation (18,797,549)      
Investment in Real Estate, Net 71,737,280      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Venn at Main [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Bellevue, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 350      
Initial Cost to Company, Land $ 26,626,498      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 151,653,323      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 139,573      
Gross Amount Carried at close of period 12/31/2017, Land 26,626,498      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 151,792,896      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 178,419,394      
Accumulated Depreciation (3,058,972)      
Investment in Real Estate, Net 175,360,422      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Vista 99 (fka Tasman) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Jose, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 554      
Initial Cost to Company, Land $ 27,709,329      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 176,023,094      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 113,479      
Gross Amount Carried at close of period 12/31/2017, Land 27,709,329      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 176,136,573      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 203,845,902      
Accumulated Depreciation (12,631,445)      
Investment in Real Estate, Net 191,214,457      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Vista Del Lago [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Mission Viejo, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 608      
Initial Cost to Company, Land $ 4,525,800      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 40,736,293      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 16,741,744      
Gross Amount Carried at close of period 12/31/2017, Land 4,525,800      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 57,478,037      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 62,003,837      
Accumulated Depreciation (46,045,156)      
Investment in Real Estate, Net 15,958,681      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Vista on Courthouse [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 220      
Initial Cost to Company, Land $ 15,550,260      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 69,449,740      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,823,317      
Gross Amount Carried at close of period 12/31/2017, Land 15,550,260      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 71,273,057      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 86,823,317      
Accumulated Depreciation (23,435,882)      
Investment in Real Estate, Net 63,387,435      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Walden Park [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Cambridge, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 232      
Initial Cost to Company, Land $ 12,448,888      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 52,044,448      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,293,327      
Gross Amount Carried at close of period 12/31/2017, Land 12,448,888      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 56,337,775      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 68,786,663      
Accumulated Depreciation (17,603,707)      
Investment in Real Estate, Net 51,182,956      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Water Park Towers [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 362      
Initial Cost to Company, Land $ 34,400,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 108,485,859      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 9,546,702      
Gross Amount Carried at close of period 12/31/2017, Land 34,400,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 118,032,561      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 152,432,561      
Accumulated Depreciation (25,460,371)      
Investment in Real Estate, Net 126,972,190      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Vintage [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Ontario, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 300      
Initial Cost to Company, Land $ 7,059,230      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 47,677,762      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,233,489      
Gross Amount Carried at close of period 12/31/2017, Land 7,059,230      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 48,911,251      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 55,970,481      
Accumulated Depreciation (20,304,558)      
Investment in Real Estate, Net 35,665,923      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Watertown Square [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Watertown, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 134      
Initial Cost to Company, Land $ 16,800,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 34,074,056      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,348,261      
Gross Amount Carried at close of period 12/31/2017, Land 16,800,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 35,422,317      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 52,222,317      
Accumulated Depreciation (7,618,267)      
Investment in Real Estate, Net 44,604,050      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
West 96th [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 207      
Initial Cost to Company, Land $ 84,800,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 67,055,502      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,265,243      
Gross Amount Carried at close of period 12/31/2017, Land 84,800,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 72,320,745      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 157,120,745      
Accumulated Depreciation (17,919,572)      
Investment in Real Estate, Net 139,201,173      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
West End Apartments (fka Emerson Place/ CRP II) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Boston, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 310      
Initial Cost to Company, Land $ 469,546      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 163,123,022      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,821,262      
Gross Amount Carried at close of period 12/31/2017, Land 469,546      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 165,944,284      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 166,413,830      
Accumulated Depreciation (55,691,880)      
Investment in Real Estate, Net 110,721,950      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Westchester at Rockville [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Rockville, MD      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 192      
Initial Cost to Company, Land $ 10,600,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 44,135,207      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 703,338      
Gross Amount Carried at close of period 12/31/2017, Land 10,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 44,838,545      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 55,438,545      
Accumulated Depreciation (9,691,644)      
Investment in Real Estate, Net 45,746,901      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Westmont [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 163      
Initial Cost to Company, Land $ 64,900,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 61,143,259      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,724,370      
Gross Amount Carried at close of period 12/31/2017, Land 64,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 63,867,629      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 128,767,629      
Accumulated Depreciation (14,415,326)      
Investment in Real Estate, Net 114,352,303      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Westside [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 204      
Initial Cost to Company, Land $ 34,200,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 56,962,630      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,861,832      
Gross Amount Carried at close of period 12/31/2017, Land 34,200,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 59,824,462      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 94,024,462      
Accumulated Depreciation (12,610,533)      
Investment in Real Estate, Net 81,413,929      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Westside Barrington (fka Westside Villas III) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 36      
Initial Cost to Company, Land $ 3,060,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 5,538,871      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 920,282      
Gross Amount Carried at close of period 12/31/2017, Land 3,060,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 6,459,153      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 9,519,153      
Accumulated Depreciation (3,618,136)      
Investment in Real Estate, Net 5,901,017      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Westside Barry (fka Westside Villas VI) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 18      
Initial Cost to Company, Land $ 1,530,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 3,023,523      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 599,854      
Gross Amount Carried at close of period 12/31/2017, Land 1,530,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 3,623,377      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 5,153,377      
Accumulated Depreciation (2,053,667)      
Investment in Real Estate, Net 3,099,710      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Westside Beloit (fka Westside Villas I) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 21      
Initial Cost to Company, Land $ 1,785,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 3,233,254      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 628,089      
Gross Amount Carried at close of period 12/31/2017, Land 1,785,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 3,861,343      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 5,646,343      
Accumulated Depreciation (2,239,628)      
Investment in Real Estate, Net 3,406,715      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Westside Bundy (fka Westside Villas II) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 23      
Initial Cost to Company, Land $ 1,955,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 3,541,435      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 642,479      
Gross Amount Carried at close of period 12/31/2017, Land 1,955,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 4,183,914      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 6,138,914      
Accumulated Depreciation (2,324,838)      
Investment in Real Estate, Net 3,814,076      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Westside Butler (fka Westside Villas IV) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 36      
Initial Cost to Company, Land $ 3,060,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 5,539,390      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 949,817      
Gross Amount Carried at close of period 12/31/2017, Land 3,060,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 6,489,207      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 9,549,207      
Accumulated Depreciation (3,619,180)      
Investment in Real Estate, Net 5,930,027      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Westside Villas (fka Westside Villas V & VII) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 113      
Initial Cost to Company, Land $ 9,605,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 19,983,385      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,493,267      
Gross Amount Carried at close of period 12/31/2017, Land 9,605,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 22,476,652      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 32,081,652      
Accumulated Depreciation (12,289,331)      
Investment in Real Estate, Net 19,792,321      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Windridge (CA) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Laguna Niguel, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 344      
Initial Cost to Company, Land $ 2,662,900      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 23,985,497      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 10,800,566      
Gross Amount Carried at close of period 12/31/2017, Land 2,662,900      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 34,786,063      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 37,448,963      
Accumulated Depreciation (25,964,327)      
Investment in Real Estate, Net 11,484,636      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Wood Creek I [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Pleasant Hill, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 256      
Initial Cost to Company, Land $ 9,729,900      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 23,009,768      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 8,661,346      
Gross Amount Carried at close of period 12/31/2017, Land 9,729,900      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 31,671,114      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 41,401,014      
Accumulated Depreciation (21,717,920)      
Investment in Real Estate, Net 19,683,094      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Management Business [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Chicago, IL      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 0      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 112,328,951      
Gross Amount Carried at close of period 12/31/2017, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 112,328,951      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 112,328,951      
Accumulated Depreciation (92,675,414)      
Investment in Real Estate, Net 19,653,537      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Operating Partnership [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Chicago, IL      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 9,047,067      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2017, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 9,047,067      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 9,047,067      
Accumulated Depreciation 0      
Investment in Real Estate, Net 9,047,067      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Other        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location N/A      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 0      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 70,353      
Gross Amount Carried at close of period 12/31/2017, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 70,353      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 70,353      
Accumulated Depreciation (15,311)      
Investment in Real Estate, Net 55,042      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Investment in Real Estate - Wholly Owned Unencumbered [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Units | ApartmentUnit 55,954      
Initial Cost to Company, Land $ 4,618,857,608      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 14,026,732,412      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,131,147,795      
Gross Amount Carried at close of period 12/31/2017, Land 4,618,857,608      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 15,157,880,207      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 19,776,737,815      
Accumulated Depreciation (4,363,244,353)      
Investment in Real Estate, Net 15,413,493,462      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
101 West End [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 506      
Initial Cost to Company, Land $ 190,600,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 131,374,708      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,465,890      
Gross Amount Carried at close of period 12/31/2017, Land 190,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 135,840,598      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 326,440,598      
Accumulated Depreciation (33,939,026)      
Investment in Real Estate, Net 292,501,572      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 103,730,409      
Joyce On Pentagon Row 1401 [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 326      
Initial Cost to Company, Land $ 9,780,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 89,668,165      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,811,215      
Gross Amount Carried at close of period 12/31/2017, Land 9,780,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 94,479,380      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 104,259,380      
Accumulated Depreciation (31,540,500)      
Investment in Real Estate, Net 72,718,880      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 57,354,529      
2501 Porter [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 202      
Initial Cost to Company, Land $ 13,000,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 75,271,179      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,572,192      
Gross Amount Carried at close of period 12/31/2017, Land 13,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 79,843,371      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 92,843,371      
Accumulated Depreciation (16,734,740)      
Investment in Real Estate, Net $ 76,108,631      
Real Estate And Accumulated Depreciation, Encumbrances Reference (J)      
300 East 39th [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 254      
Initial Cost to Company, Land $ 48,900,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 96,174,639      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,532,467      
Gross Amount Carried at close of period 12/31/2017, Land 48,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 99,707,106      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 148,607,106      
Accumulated Depreciation (21,799,732)      
Investment in Real Estate, Net 126,807,374      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 60,451,283      
303 East 83rd (fka Camargue) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 261      
Initial Cost to Company, Land $ 79,400,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 79,122,624      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,673,574      
Gross Amount Carried at close of period 12/31/2017, Land 79,400,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 82,796,198      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 162,196,198      
Accumulated Depreciation (18,995,345)      
Investment in Real Estate, Net $ 143,200,853      
Real Estate And Accumulated Depreciation, Encumbrances Reference (J)      
425 Broadway [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Santa Monica, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 101      
Initial Cost to Company, Land $ 12,600,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 34,394,772      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,577,985      
Gross Amount Carried at close of period 12/31/2017, Land 12,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 37,972,757      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 50,572,757      
Accumulated Depreciation (8,081,082)      
Investment in Real Estate, Net $ 42,491,675      
Real Estate And Accumulated Depreciation, Encumbrances Reference (J)      
55 West Fifth I & II (fka Townhouse Plaza and Gardens)s [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Mateo, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 241      
Initial Cost to Company, Land $ 21,041,710      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 71,931,323      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 12,415,912      
Gross Amount Carried at close of period 12/31/2017, Land 21,041,710      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 84,347,235      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 105,388,945      
Accumulated Depreciation (21,523,119)      
Investment in Real Estate, Net 83,865,826      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 26,356,053      
800 Sixth Ave (fka Chelsea) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 266      
Initial Cost to Company, Land $ 59,900,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 155,861,605      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,180,446      
Gross Amount Carried at close of period 12/31/2017, Land 59,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 158,042,051      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 217,942,051      
Accumulated Depreciation (32,855,478)      
Investment in Real Estate, Net 185,086,573      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 77,654,125      
Alcyone [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 162      
Initial Cost to Company, Land $ 11,379,497      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 49,360,503      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 973,758      
Gross Amount Carried at close of period 12/31/2017, Land 11,379,497      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 50,334,261      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 61,713,758      
Accumulated Depreciation (7,663,311)      
Investment in Real Estate, Net 54,050,447      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 28,247,417      
929 Mass (fka 929 House) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Cambridge, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 127      
Initial Cost to Company, Land $ 3,252,993      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 21,745,595      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,801,241      
Gross Amount Carried at close of period 12/31/2017, Land 3,252,993      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 28,546,836      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 31,799,829      
Accumulated Depreciation (17,379,493)      
Investment in Real Estate, Net 14,420,336      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 578,381      
Arches, The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Sunnyvale, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 410      
Initial Cost to Company, Land $ 26,650,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 62,850,000      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,807,099      
Gross Amount Carried at close of period 12/31/2017, Land 26,650,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 64,657,099      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 91,307,099      
Accumulated Depreciation (20,704,043)      
Investment in Real Estate, Net $ 70,603,056      
Real Estate And Accumulated Depreciation, Encumbrances Reference (I)      
Academy Village [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location North Hollywood, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 248      
Initial Cost to Company, Land $ 25,000,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 23,593,194      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 8,511,551      
Gross Amount Carried at close of period 12/31/2017, Land 25,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 32,104,745      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 57,104,745      
Accumulated Depreciation (18,102,739)      
Investment in Real Estate, Net 39,002,006      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 19,965,907      
Artisan Square [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Northridge, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 140      
Initial Cost to Company, Land $ 7,000,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 20,537,359      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,462,204      
Gross Amount Carried at close of period 12/31/2017, Land 7,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 21,999,563      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 28,999,563      
Accumulated Depreciation (11,523,867)      
Investment in Real Estate, Net 17,475,696      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 22,757,833      
Avanti [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Anaheim, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 162      
Initial Cost to Company, Land $ 12,960,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 18,497,682      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,682,239      
Gross Amount Carried at close of period 12/31/2017, Land 12,960,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 22,179,921      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 35,139,921      
Accumulated Depreciation (9,463,903)      
Investment in Real Estate, Net 25,676,018      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 25,012,978      
Avenir [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Boston, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 241      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 114,321,618      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,981,881      
Gross Amount Carried at close of period 12/31/2017, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 116,303,499      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 116,303,499      
Accumulated Depreciation (24,093,714)      
Investment in Real Estate, Net 92,209,785      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 88,921,043      
Bella Vista Apartments at Boca Del Mar [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Woodland Hills, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 579      
Initial Cost to Company, Land $ 31,682,754      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 121,095,786      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,014,382      
Gross Amount Carried at close of period 12/31/2017, Land 31,682,754      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 127,110,168      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 158,792,922      
Accumulated Depreciation (53,777,824)      
Investment in Real Estate, Net 105,015,098      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 57,907,496      
Berkeleyan [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Berkeley, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 56      
Initial Cost to Company, Land $ 4,377,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 16,022,110      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 382,895      
Gross Amount Carried at close of period 12/31/2017, Land 4,377,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 16,405,005      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 20,782,005      
Accumulated Depreciation (6,678,279)      
Investment in Real Estate, Net 14,103,726      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 8,194,316      
Calvert Woodley [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 136      
Initial Cost to Company, Land $ 12,600,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 43,527,379      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,058,223      
Gross Amount Carried at close of period 12/31/2017, Land 12,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 45,585,602      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 58,185,602      
Accumulated Depreciation (10,036,657)      
Investment in Real Estate, Net $ 48,148,945      
Real Estate And Accumulated Depreciation, Encumbrances Reference (J)      
Carmel Terrace [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Diego, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 384      
Initial Cost to Company, Land $ 2,288,300      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 20,596,281      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 11,891,883      
Gross Amount Carried at close of period 12/31/2017, Land 2,288,300      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 32,488,164      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 34,776,464      
Accumulated Depreciation (26,616,700)      
Investment in Real Estate, Net $ 8,159,764      
Real Estate And Accumulated Depreciation, Encumbrances Reference (I)      
Chelsea Square [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Redmond, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 113      
Initial Cost to Company, Land $ 3,397,100      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 9,289,074      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,525,829      
Gross Amount Carried at close of period 12/31/2017, Land 3,397,100      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 11,814,903      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 15,212,003      
Accumulated Depreciation (7,732,982)      
Investment in Real Estate, Net 7,479,021      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 9,219,668      
Citrus Suites [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Santa Monica, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 70      
Initial Cost to Company, Land $ 9,000,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 16,950,326      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,886,846      
Gross Amount Carried at close of period 12/31/2017, Land 9,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 18,837,172      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 27,837,172      
Accumulated Depreciation (4,064,530)      
Investment in Real Estate, Net $ 23,772,642      
Real Estate And Accumulated Depreciation, Encumbrances Reference (J)      
Cleveland House [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 214      
Initial Cost to Company, Land $ 18,300,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 66,392,414      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,953,014      
Gross Amount Carried at close of period 12/31/2017, Land 18,300,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 70,345,428      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 88,645,428      
Accumulated Depreciation (15,198,718)      
Investment in Real Estate, Net $ 73,446,710      
Real Estate And Accumulated Depreciation, Encumbrances Reference (J)      
Columbia Crossing [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 247      
Initial Cost to Company, Land $ 23,500,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 53,045,073      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,637,583      
Gross Amount Carried at close of period 12/31/2017, Land 23,500,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 55,682,656      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 79,182,656      
Accumulated Depreciation (12,776,595)      
Investment in Real Estate, Net $ 66,406,061      
Real Estate And Accumulated Depreciation, Encumbrances Reference (J)      
Deerwood (SD) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Diego, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 316      
Initial Cost to Company, Land $ 2,082,095      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 18,739,815      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 14,811,438      
Gross Amount Carried at close of period 12/31/2017, Land 2,082,095      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 33,551,253      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 35,633,348      
Accumulated Depreciation (28,255,938)      
Investment in Real Estate, Net $ 7,377,410      
Real Estate And Accumulated Depreciation, Encumbrances Reference (I)      
DelMarRidge [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Diego, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 181      
Initial Cost to Company, Land $ 7,801,824      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 36,948,176      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,819,678      
Gross Amount Carried at close of period 12/31/2017, Land 7,801,824      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 40,767,854      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 48,569,678      
Accumulated Depreciation (14,687,909)      
Investment in Real Estate, Net 33,881,769      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 39,502,426      
Estancia at Santa Clara (fka Santa Clara) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Santa Clara, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 450      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 123,759,804      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,306,632      
Gross Amount Carried at close of period 12/31/2017, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 125,066,436      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 125,066,436      
Accumulated Depreciation (27,568,376)      
Investment in Real Estate, Net $ 97,498,060      
Real Estate And Accumulated Depreciation, Encumbrances Reference (J)      
Fairchase [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Fairfax, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 392      
Initial Cost to Company, Land $ 23,500,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 87,722,321      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 956,574      
Gross Amount Carried at close of period 12/31/2017, Land 23,500,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 88,678,895      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 112,178,895      
Accumulated Depreciation (18,576,327)      
Investment in Real Estate, Net $ 93,602,568      
Real Estate And Accumulated Depreciation, Encumbrances Reference (J)      
Fairfield [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Stamford, CT      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 263      
Initial Cost to Company, Land $ 6,510,200      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 39,690,120      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,711,222      
Gross Amount Carried at close of period 12/31/2017, Land 6,510,200      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 47,401,342      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 53,911,542      
Accumulated Depreciation (32,614,560)      
Investment in Real Estate, Net 21,296,982      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 31,314,687      
Fine Arts Building [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Berkeley, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 100      
Initial Cost to Company, Land $ 7,817,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 26,462,772      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 379,630      
Gross Amount Carried at close of period 12/31/2017, Land 7,817,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 26,842,402      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 34,659,402      
Accumulated Depreciation (10,821,726)      
Investment in Real Estate, Net 23,837,676      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 15,964,066      
Flats at DuPont Circle [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 306      
Initial Cost to Company, Land $ 35,200,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 108,768,198      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,152,022      
Gross Amount Carried at close of period 12/31/2017, Land 35,200,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 109,920,220      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 145,120,220      
Accumulated Depreciation (22,256,517)      
Investment in Real Estate, Net $ 122,863,703      
Real Estate And Accumulated Depreciation, Encumbrances Reference (J)      
Gaia Building [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Berkeley, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 91      
Initial Cost to Company, Land $ 7,113,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 25,623,826      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 317,100      
Gross Amount Carried at close of period 12/31/2017, Land 7,113,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 25,940,926      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 33,053,926      
Accumulated Depreciation (10,427,553)      
Investment in Real Estate, Net 22,626,373      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 14,501,551      
Gaithersburg Station [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Gaithersburg, MD      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 389      
Initial Cost to Company, Land $ 17,500,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 74,678,917      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 814,507      
Gross Amount Carried at close of period 12/31/2017, Land 17,500,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 75,493,424      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 92,993,424      
Accumulated Depreciation (15,197,790)      
Investment in Real Estate, Net 77,795,634      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 95,368,543      
Glo [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 201      
Initial Cost to Company, Land $ 16,047,022      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 48,650,963      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,068,235      
Gross Amount Carried at close of period 12/31/2017, Land 16,047,022      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 51,719,198      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 67,766,220      
Accumulated Depreciation (14,061,824)      
Investment in Real Estate, Net 53,704,396      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 32,031,227      
Hathaway [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Long Beach, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 385      
Initial Cost to Company, Land $ 2,512,500      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 22,611,912      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 9,165,543      
Gross Amount Carried at close of period 12/31/2017, Land 2,512,500      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 31,777,455      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 34,289,955      
Accumulated Depreciation (24,359,922)      
Investment in Real Estate, Net 9,930,033      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 46,479,980      
Heights on Capitol Hill [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 104      
Initial Cost to Company, Land $ 5,425,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 21,138,028      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,483,284      
Gross Amount Carried at close of period 12/31/2017, Land 5,425,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 22,621,312      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 28,046,312      
Accumulated Depreciation (9,090,011)      
Investment in Real Estate, Net 18,956,301      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 25,887,074      
Kelvin Court (fka Alta Pacific) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Irvine, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 132      
Initial Cost to Company, Land $ 10,752,145      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 34,628,115      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 648,366      
Gross Amount Carried at close of period 12/31/2017, Land 10,752,145      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 35,276,481      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 46,028,626      
Accumulated Depreciation (11,953,874)      
Investment in Real Estate, Net 34,074,752      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 26,226,033      
Kenwood Mews [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Burbank, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 141      
Initial Cost to Company, Land $ 14,100,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 24,662,883      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,580,534      
Gross Amount Carried at close of period 12/31/2017, Land 14,100,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 28,243,417      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 42,343,417      
Accumulated Depreciation (12,733,507)      
Investment in Real Estate, Net $ 29,609,910      
Real Estate And Accumulated Depreciation, Encumbrances Reference (I)      
La Terrazza at Colma Station [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Colma, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 155      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 41,251,044      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,206,497      
Gross Amount Carried at close of period 12/31/2017, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 42,457,541      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 42,457,541      
Accumulated Depreciation (16,832,082)      
Investment in Real Estate, Net 25,625,459      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 24,987,438      
Laguna Clara [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Santa Clara, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 264      
Initial Cost to Company, Land $ 13,642,420      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 29,707,475      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,969,596      
Gross Amount Carried at close of period 12/31/2017, Land 13,642,420      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 34,677,071      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 48,319,491      
Accumulated Depreciation (18,383,225)      
Investment in Real Estate, Net $ 29,936,266      
Real Estate And Accumulated Depreciation, Encumbrances Reference (I)      
Liberty Park [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Braintree, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 202      
Initial Cost to Company, Land $ 5,977,504      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 26,749,111      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,357,010      
Gross Amount Carried at close of period 12/31/2017, Land 5,977,504      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 33,106,121      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 39,083,625      
Accumulated Depreciation (17,080,472)      
Investment in Real Estate, Net 22,003,153      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 24,956,877      
Liberty Tower [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 235      
Initial Cost to Company, Land $ 16,382,822      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 83,817,078      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,975,311      
Gross Amount Carried at close of period 12/31/2017, Land 16,382,822      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 85,792,389      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 102,175,211      
Accumulated Depreciation (26,194,514)      
Investment in Real Estate, Net 75,980,697      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 43,515,440      
Longview Place [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Waltham, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 348      
Initial Cost to Company, Land $ 20,880,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 90,255,509      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,422,745      
Gross Amount Carried at close of period 12/31/2017, Land 20,880,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 95,678,254      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 116,558,254      
Accumulated Depreciation (41,854,802)      
Investment in Real Estate, Net 74,703,452      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 70,793,963      
Market Street Village [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Diego, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 229      
Initial Cost to Company, Land $ 13,740,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 40,757,301      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,123,013      
Gross Amount Carried at close of period 12/31/2017, Land 13,740,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 42,880,314      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 56,620,314      
Accumulated Depreciation (18,041,199)      
Investment in Real Estate, Net $ 38,579,115      
Real Estate And Accumulated Depreciation, Encumbrances Reference (I)      
Metro on First [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 102      
Initial Cost to Company, Land $ 8,540,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 12,209,981      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,141,118      
Gross Amount Carried at close of period 12/31/2017, Land 8,540,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 14,351,099      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 22,891,099      
Accumulated Depreciation (5,948,086)      
Investment in Real Estate, Net 16,943,013      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 22,629,291      
Mill Creek [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Milpitas, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 516      
Initial Cost to Company, Land $ 12,858,693      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 57,168,503      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 9,899,985      
Gross Amount Carried at close of period 12/31/2017, Land 12,858,693      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 67,068,488      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 79,927,181      
Accumulated Depreciation (33,621,630)      
Investment in Real Estate, Net 46,305,551      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 69,262,254      
Moda [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 251      
Initial Cost to Company, Land $ 12,649,228      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 36,842,012      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,017,073      
Gross Amount Carried at close of period 12/31/2017, Land 12,649,228      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 37,859,085      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 50,508,313      
Accumulated Depreciation (12,489,032)      
Investment in Real Estate, Net $ 38,019,281      
Real Estate And Accumulated Depreciation, Encumbrances Reference (K)      
Montierra (CA) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Diego, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 272      
Initial Cost to Company, Land $ 8,160,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 29,360,938      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,947,448      
Gross Amount Carried at close of period 12/31/2017, Land 8,160,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 37,308,386      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 45,468,386      
Accumulated Depreciation (24,130,197)      
Investment in Real Estate, Net $ 21,338,189      
Real Estate And Accumulated Depreciation, Encumbrances Reference (I)      
Olympus Towers [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 328      
Initial Cost to Company, Land $ 14,752,034      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 73,335,425      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 8,745,325      
Gross Amount Carried at close of period 12/31/2017, Land 14,752,034      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 82,080,750      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 96,832,784      
Accumulated Depreciation (39,929,257)      
Investment in Real Estate, Net 56,903,527      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 49,788,935      
Park Place at San Mateo (fka San Mateo) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Mateo, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 575      
Initial Cost to Company, Land $ 71,900,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 211,907,141      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 11,404,928      
Gross Amount Carried at close of period 12/31/2017, Land 71,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 223,312,069      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 295,212,069      
Accumulated Depreciation (47,760,787)      
Investment in Real Estate, Net $ 247,451,282      
Real Estate And Accumulated Depreciation, Encumbrances Reference (J)      
Reserve at Clarendon Centre, The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 252      
Initial Cost to Company, Land $ 10,500,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 52,812,935      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,599,506      
Gross Amount Carried at close of period 12/31/2017, Land 10,500,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 57,412,441      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 67,912,441      
Accumulated Depreciation (28,603,885)      
Investment in Real Estate, Net $ 39,308,556      
Real Estate And Accumulated Depreciation, Encumbrances Reference (I)      
Reserve at Eisenhower, The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Alexandria, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 226      
Initial Cost to Company, Land $ 6,500,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 34,585,060      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,865,452      
Gross Amount Carried at close of period 12/31/2017, Land 6,500,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 38,450,512      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 44,950,512      
Accumulated Depreciation (19,227,311)      
Investment in Real Estate, Net $ 25,723,201      
Real Estate And Accumulated Depreciation, Encumbrances Reference (I)      
Reserve at Fairfax Corners [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Fairfax, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 652      
Initial Cost to Company, Land $ 15,804,057      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 63,129,051      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 11,326,169      
Gross Amount Carried at close of period 12/31/2017, Land 15,804,057      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 74,455,220      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 90,259,277      
Accumulated Depreciation (38,763,866)      
Investment in Real Estate, Net 51,495,411      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 84,677,136      
Siena Terrace [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Lake Forest, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 356      
Initial Cost to Company, Land $ 8,900,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 24,083,024      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,129,612      
Gross Amount Carried at close of period 12/31/2017, Land 8,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 31,212,636      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 40,112,636      
Accumulated Depreciation (20,109,124)      
Investment in Real Estate, Net 20,003,512      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 64,414,512      
SoMa Square Apartments (fka South Market) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Francisco, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 410      
Initial Cost to Company, Land $ 79,900,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 177,316,977      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 9,300,349      
Gross Amount Carried at close of period 12/31/2017, Land 79,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 186,617,326      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 266,517,326      
Accumulated Depreciation (38,289,333)      
Investment in Real Estate, Net $ 228,227,993      
Real Estate And Accumulated Depreciation, Encumbrances Reference (J)      
Skyview [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Rancho Santa Margarita, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 260      
Initial Cost to Company, Land $ 3,380,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 21,952,863      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,298,716      
Gross Amount Carried at close of period 12/31/2017, Land 3,380,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 27,251,579      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 30,631,579      
Accumulated Depreciation (16,612,037)      
Investment in Real Estate, Net 14,019,542      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 47,183,965      
Square One [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 112      
Initial Cost to Company, Land $ 7,222,544      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 26,277,456      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 29,629      
Gross Amount Carried at close of period 12/31/2017, Land 7,222,544      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 26,307,085      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 33,529,629      
Accumulated Depreciation (4,313,830)      
Investment in Real Estate, Net $ 29,215,799      
Real Estate And Accumulated Depreciation, Encumbrances Reference (K)      
Summerset Village [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Chatsworth, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 280      
Initial Cost to Company, Land $ 2,629,804      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 23,670,889      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,787,016      
Gross Amount Carried at close of period 12/31/2017, Land 2,629,804      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 31,457,905      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 34,087,709      
Accumulated Depreciation (22,465,064)      
Investment in Real Estate, Net 11,622,645      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 38,007,297      
Talleyrand [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Tarrytown, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 300      
Initial Cost to Company, Land $ 12,000,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 49,838,160      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,352,043      
Gross Amount Carried at close of period 12/31/2017, Land 12,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 56,190,203      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 68,190,203      
Accumulated Depreciation (31,701,891)      
Investment in Real Estate, Net 36,488,312      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 34,811,455      
Teresina [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Chula Vista, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 440      
Initial Cost to Company, Land $ 28,600,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 61,916,670      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,715,027      
Gross Amount Carried at close of period 12/31/2017, Land 28,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 67,631,697      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 96,231,697      
Accumulated Depreciation (29,443,097)      
Investment in Real Estate, Net 66,788,600      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 38,425,773      
Toscana [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Irvine, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 563      
Initial Cost to Company, Land $ 39,410,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 50,806,072      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 17,577,052      
Gross Amount Carried at close of period 12/31/2017, Land 39,410,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 68,383,124      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 107,793,124      
Accumulated Depreciation (37,833,043)      
Investment in Real Estate, Net 69,960,081      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 98,047,399      
Touriel Building [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Berkeley, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 35      
Initial Cost to Company, Land $ 2,736,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 7,810,027      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 186,222      
Gross Amount Carried at close of period 12/31/2017, Land 2,736,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 7,996,249      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 10,732,249      
Accumulated Depreciation (3,315,964)      
Investment in Real Estate, Net 7,416,285      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 4,969,645      
Town Square at Mark Center I (fka Millbrook I) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Alexandria, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 406      
Initial Cost to Company, Land $ 24,360,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 86,178,714      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,407,814      
Gross Amount Carried at close of period 12/31/2017, Land 24,360,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 93,586,528      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 117,946,528      
Accumulated Depreciation (41,076,185)      
Investment in Real Estate, Net 76,870,343      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 60,225,838      
Vantage Hollywood [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 298      
Initial Cost to Company, Land $ 42,580,326      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 56,014,674      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 457,365      
Gross Amount Carried at close of period 12/31/2017, Land 42,580,326      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 56,472,039      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 99,052,365      
Accumulated Depreciation (7,801,330)      
Investment in Real Estate, Net 91,251,035      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 41,416,137      
Versailles [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Woodland Hills, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 253      
Initial Cost to Company, Land $ 12,650,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 33,656,292      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,159,381      
Gross Amount Carried at close of period 12/31/2017, Land 12,650,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 40,815,673      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 53,465,673      
Accumulated Depreciation (21,305,317)      
Investment in Real Estate, Net 32,160,356      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 30,347,501      
Versailles (K-Town) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 225      
Initial Cost to Company, Land $ 10,590,975      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 44,409,025      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,547,377      
Gross Amount Carried at close of period 12/31/2017, Land 10,590,975      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 45,956,402      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 56,547,377      
Accumulated Depreciation (15,658,207)      
Investment in Real Estate, Net 40,889,170      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 45,964,864      
Victor on Venice [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 115      
Initial Cost to Company, Land $ 10,350,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 35,433,437      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 797,872      
Gross Amount Carried at close of period 12/31/2017, Land 10,350,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 36,231,309      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 46,581,309      
Accumulated Depreciation (14,701,990)      
Investment in Real Estate, Net $ 31,879,319      
Real Estate And Accumulated Depreciation, Encumbrances Reference (I)      
Vintage at 425 Broadway (fka Promenade) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Santa Monica, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 60      
Initial Cost to Company, Land $ 9,000,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 13,961,523      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,555,558      
Gross Amount Carried at close of period 12/31/2017, Land 9,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 15,517,081      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 24,517,081      
Accumulated Depreciation (3,564,636)      
Investment in Real Estate, Net $ 20,952,445      
Real Estate And Accumulated Depreciation, Encumbrances Reference (J)      
West 54th [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 222      
Initial Cost to Company, Land $ 60,900,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 48,193,837      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,225,501      
Gross Amount Carried at close of period 12/31/2017, Land 60,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 51,419,338      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 112,319,338      
Accumulated Depreciation (12,886,577)      
Investment in Real Estate, Net 99,432,761      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 47,667,759      
Westgate (fka Westgate I) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Pasadena, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 480      
Initial Cost to Company, Land $ 22,898,848      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 133,484,573      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,262,866      
Gross Amount Carried at close of period 12/31/2017, Land 22,898,848      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 135,747,439      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 158,646,287      
Accumulated Depreciation (32,510,875)      
Investment in Real Estate, Net 126,135,412      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 95,981,749      
Woodleaf [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Campbell, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 178      
Initial Cost to Company, Land $ 8,550,600      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 16,988,183      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,069,445      
Gross Amount Carried at close of period 12/31/2017, Land 8,550,600      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 22,057,628      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 30,608,228      
Accumulated Depreciation (14,254,057)      
Investment in Real Estate, Net 16,354,171      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 17,819,380      
Portfolio Entity Encumbrances [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Units | ApartmentUnit      
Initial Cost to Company, Land      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures      
Gross Amount Carried at close of period 12/31/2017, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures      
Accumulated Depreciation      
Investment in Real Estate, Net      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 1,346,853,789      
Investment in Real Estate - Wholly Owned Encumbered [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Units | ApartmentUnit 18,497      
Initial Cost to Company, Land $ 1,401,915,995      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 3,881,590,219      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 316,875,095      
Gross Amount Carried at close of period 12/31/2017, Land 1,401,915,995      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 4,198,465,314      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 5,600,381,309      
Accumulated Depreciation (1,440,591,113)      
Investment in Real Estate, Net 4,159,790,196      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 3,316,375,422      
2300 Elliott [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 92      
Initial Cost to Company, Land $ 796,800      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 7,173,725      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,717,795      
Gross Amount Carried at close of period 12/31/2017, Land 796,800      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 13,891,520      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 14,688,320      
Accumulated Depreciation (10,921,953)      
Investment in Real Estate, Net 3,766,367      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Canyon Ridge [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Diego, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 162      
Initial Cost to Company, Land $ 4,869,448      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 11,955,064      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,954,912      
Gross Amount Carried at close of period 12/31/2017, Land 4,869,448      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 15,909,976      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 20,779,424      
Accumulated Depreciation (10,552,909)      
Investment in Real Estate, Net 10,226,515      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Country Oaks [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Agoura Hills, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 256      
Initial Cost to Company, Land $ 6,105,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 29,561,865      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,647,900      
Gross Amount Carried at close of period 12/31/2017, Land 6,105,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 36,209,765      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 42,314,765      
Accumulated Depreciation (19,712,219)      
Investment in Real Estate, Net 22,602,546      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Harrison Square (fka Elliot Bay) [Domain]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 166      
Initial Cost to Company, Land $ 7,600,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 35,844,345      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,069,730      
Gross Amount Carried at close of period 12/31/2017, Land 7,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 40,914,075      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 48,514,075      
Accumulated Depreciation (9,358,506)      
Investment in Real Estate, Net 39,155,569      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Monterra in Mill Creek [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Mill Creek, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 139      
Initial Cost to Company, Land $ 2,800,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 13,255,123      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,003,101      
Gross Amount Carried at close of period 12/31/2017, Land 2,800,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 14,258,224      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 17,058,224      
Accumulated Depreciation (6,620,281)      
Investment in Real Estate, Net 10,437,943      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Rosecliff [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Quincy, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 156      
Initial Cost to Company, Land $ 5,460,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 15,721,570      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,530,721      
Gross Amount Carried at close of period 12/31/2017, Land 5,460,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 19,252,291      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 24,712,291      
Accumulated Depreciation (12,249,762)      
Investment in Real Estate, Net 12,462,529      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Strayhorse at Arrowhead Ranch [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Glendale, AZ      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 136      
Initial Cost to Company, Land $ 4,400,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 12,968,002      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 802,003      
Gross Amount Carried at close of period 12/31/2017, Land 4,400,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 13,770,005      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 18,170,005      
Accumulated Depreciation (6,164,596)      
Investment in Real Estate, Net 12,005,409      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Via Ventura (CA) (fka Ventura) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Ventura, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 192      
Initial Cost to Company, Land $ 8,600,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 44,308,202      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 845,940      
Gross Amount Carried at close of period 12/31/2017, Land 8,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 45,154,142      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 53,754,142      
Accumulated Depreciation (10,983,822)      
Investment in Real Estate, Net 42,770,320      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Wood Creek II (fka Willow Brook (CA))        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Pleasant Hill, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 228      
Initial Cost to Company, Land $ 5,055,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 38,388,672      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,551,944      
Gross Amount Carried at close of period 12/31/2017, Land 5,055,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 44,940,616      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 49,995,616      
Accumulated Depreciation (22,087,591)      
Investment in Real Estate, Net 27,908,025      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Investment in Real Estate - Partially Owned Unencumbered [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Units | ApartmentUnit 1,527      
Initial Cost to Company, Land $ 45,686,248      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 209,176,568      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 35,124,046      
Gross Amount Carried at close of period 12/31/2017, Land 45,686,248      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 244,300,614      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 289,986,862      
Accumulated Depreciation (108,651,639)      
Investment in Real Estate, Net 181,335,223      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Bellevue Meadows [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Bellevue, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 180      
Initial Cost to Company, Land $ 4,507,100      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 12,574,814      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,487,604      
Gross Amount Carried at close of period 12/31/2017, Land 4,507,100      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 18,062,418      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 22,569,518      
Accumulated Depreciation (12,705,342)      
Investment in Real Estate, Net 9,864,176      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 16,504,927      
Canyon Creek (CA) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Ramon, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 268      
Initial Cost to Company, Land $ 5,425,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 18,812,120      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,580,209      
Gross Amount Carried at close of period 12/31/2017, Land 5,425,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 26,392,329      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 31,817,329      
Accumulated Depreciation (16,113,349)      
Investment in Real Estate, Net 15,703,980      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 28,129,557      
Lantern Cove [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Foster City, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 232      
Initial Cost to Company, Land $ 6,945,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 23,064,976      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,401,023      
Gross Amount Carried at close of period 12/31/2017, Land 6,945,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 29,465,999      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 36,410,999      
Accumulated Depreciation (17,362,236)      
Investment in Real Estate, Net 19,048,763      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 36,410,267      
Schooner Bay I [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Foster City, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 168      
Initial Cost to Company, Land $ 5,345,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 20,390,618      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,132,524      
Gross Amount Carried at close of period 12/31/2017, Land 5,345,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 25,523,142      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 30,868,142      
Accumulated Depreciation (15,015,057)      
Investment in Real Estate, Net 15,853,085      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 28,825,496      
Schooner Bay II [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Foster City, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 144      
Initial Cost to Company, Land $ 4,550,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 18,064,764      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,600,065      
Gross Amount Carried at close of period 12/31/2017, Land 4,550,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 22,664,829      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 27,214,829      
Accumulated Depreciation (13,411,541)      
Investment in Real Estate, Net 13,803,288      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 26,130,631      
Surrey Downs [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Bellevue, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 122      
Initial Cost to Company, Land $ 3,057,100      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 7,848,618      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,159,103      
Gross Amount Carried at close of period 12/31/2017, Land 3,057,100      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 11,007,721      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 14,064,821      
Accumulated Depreciation (7,377,616)      
Investment in Real Estate, Net 6,687,205      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 9,810,499      
Virgil Square [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 142      
Initial Cost to Company, Land $ 5,500,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 15,216,613      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,890,085      
Gross Amount Carried at close of period 12/31/2017, Land 5,500,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 18,106,698      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 23,606,698      
Accumulated Depreciation (8,612,798)      
Investment in Real Estate, Net 14,993,900      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 9,877,693      
Wisconsin Place [Domain]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Chevy Chase, MD      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 432      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 172,089,355      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,148,714      
Gross Amount Carried at close of period 12/31/2017, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 173,238,069      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 173,238,069      
Accumulated Depreciation (37,293,147)      
Investment in Real Estate, Net 135,944,922      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 146,657,506      
Investment in Real Estate - Partially Owned Encumbered [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Units | ApartmentUnit 1,688      
Initial Cost to Company, Land $ 35,329,200      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 288,061,878      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 36,399,327      
Gross Amount Carried at close of period 12/31/2017, Land 35,329,200      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 324,461,205      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 359,790,405      
Accumulated Depreciation (127,891,086)      
Investment in Real Estate, Net 231,899,319      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 302,346,576      
Total Consolidated Investment in Real Estate [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Units | ApartmentUnit 77,666      
Initial Cost to Company, Land $ 6,101,789,051      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 18,405,561,077      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,519,546,263      
Gross Amount Carried at close of period 12/31/2017, Land 6,101,789,051      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 19,925,107,340      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 26,026,896,391      
Accumulated Depreciation (6,040,378,191)      
Investment in Real Estate, Net 19,986,518,200      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 3,618,721,998