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Schedule III - Real Estate and Accumulated Depreciation (Details)
 12 Months Ended
Dec. 31, 2018
USD ($)
ApartmentUnit
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Real Estate And Accumulated Depreciation Abstract        
Accumulated Depreciation $ (6,696,281,000) $ (6,040,378,000) $ (5,360,389,000) $ (6,084,616,000)
100 K Apartments (fka 100K 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 222      
Initial Cost to Company, Land $ 15,600,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 69,516,265      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2018, Land 15,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 69,516,265      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 85,116,265      
Accumulated Depreciation (270,039)      
Investment in Real Estate, Net 84,846,226      
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 9,479,410      
Gross Amount Carried at close of period 12/31/2018, Land 103,539,100      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 103,562,135      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 207,101,235      
Accumulated Depreciation (48,691,122)      
Investment in Real Estate, Net 158,410,113      
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 15,656,370      
Gross Amount Carried at close of period 12/31/2018, Land 139,933,500      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 206,621,115      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 346,554,615      
Accumulated Depreciation (96,815,700)      
Investment in Real Estate, Net 249,738,915      
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 112,096,955      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 235,580      
Gross Amount Carried at close of period 12/31/2018, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 112,332,535      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 112,332,535      
Accumulated Depreciation (16,016,094)      
Investment in Real Estate, Net 96,316,441      
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 1,701,936      
Gross Amount Carried at close of period 12/31/2018, Land 22,037,831      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 55,664,105      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 77,701,936      
Accumulated Depreciation (16,317,361)      
Investment in Real Estate, Net 61,384,575      
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 3,859,381      
Gross Amount Carried at close of period 12/31/2018, Land 32,400,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 96,534,609      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 128,934,609      
Accumulated Depreciation (23,584,176)      
Investment in Real Estate, Net 105,350,433      
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 13,831,031      
Gross Amount Carried at close of period 12/31/2018, Land 144,968,250      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 152,177,712      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 297,145,962      
Accumulated Depreciation (72,790,895)      
Investment in Real Estate, Net 224,355,067      
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 94,758,679      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 278,928      
Gross Amount Carried at close of period 12/31/2018, Land 18,937,702      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 95,037,607      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 113,975,309      
Accumulated Depreciation (22,340,533)      
Investment in Real Estate, Net 91,634,776      
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 $ 9,213,512      
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 2,537,398      
Gross Amount Carried at close of period 12/31/2018, Land 9,213,512      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 39,096,587      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 48,310,099      
Accumulated Depreciation (18,478,163)      
Investment in Real Estate, Net 29,831,936      
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 24,121,307      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2018, Land 10,401,958      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 24,121,307      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 34,523,265      
Accumulated Depreciation 0      
Investment in Real Estate, Net 34,523,265      
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 15,209,807      
Gross Amount Carried at close of period 12/31/2018, Land 54,638,298      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 55,571,509      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 110,209,807      
Accumulated Depreciation (26,934,077)      
Investment in Real Estate, Net 83,275,730      
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 6,217,218      
Gross Amount Carried at close of period 12/31/2018, Land 31,400,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 115,222,952      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 146,622,952      
Accumulated Depreciation (28,057,310)      
Investment in Real Estate, Net 118,565,642      
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 2,567,690      
Gross Amount Carried at close of period 12/31/2018, Land 11,321,198      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 52,241,865      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 63,563,063      
Accumulated Depreciation (13,457,087)      
Investment in Real Estate, Net 50,105,976      
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 3,697,727      
Gross Amount Carried at close of period 12/31/2018, Land 21,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 82,422,390      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 104,322,390      
Accumulated Depreciation (20,152,746)      
Investment in Real Estate, Net 84,169,644      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
2400 M St [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 4,562,289      
Gross Amount Carried at close of period 12/31/2018, Land 30,006,593      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 118,576,074      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 148,582,667      
Accumulated Depreciation (53,570,540)      
Investment in Real Estate, Net 95,012,127      
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 21,564,301      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2018, Land 4,603,326      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 21,564,301      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 26,167,627      
Accumulated Depreciation 0      
Investment in Real Estate, Net 26,167,627      
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 766,896      
Gross Amount Carried at close of period 12/31/2018, Land 14,450,070      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 116,591,826      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 131,041,896      
Accumulated Depreciation (18,672,172)      
Investment in Real Estate, Net 112,369,724      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
340 Fremont (fka Rincon Hill) [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 247,811,082      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 92,829      
Gross Amount Carried at close of period 12/31/2018, Land 42,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 247,903,911      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 289,903,911      
Accumulated Depreciation (23,751,926)      
Investment in Real Estate, Net 266,151,985      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
3003 Van Ness (fka 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 6,576,256      
Gross Amount Carried at close of period 12/31/2018, Land 56,300,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 147,767,836      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 204,067,836      
Accumulated Depreciation (38,475,875)      
Investment in Real Estate, Net 165,591,961      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
45 Worthington (City View 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 0      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 2,644,777      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2018, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 2,644,777      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 2,644,777      
Accumulated Depreciation 0      
Investment in Real Estate, Net 2,644,777      
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 4,379,551      
Gross Amount Carried at close of period 12/31/2018, Land 28,150,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 142,979,551      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 171,129,551      
Accumulated Depreciation (48,799,382)      
Investment in Real Estate, Net 122,330,169      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
455 Eye 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 $ 11,941,406      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 61,395,797      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 20,856      
Gross Amount Carried at close of period 12/31/2018, Land 11,941,406      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 61,416,653      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 73,358,059      
Accumulated Depreciation (3,530,514)      
Investment in Real Estate, Net 69,827,545      
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 30,602,147      
Gross Amount Carried at close of period 12/31/2018, Land 76,921,130      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 184,549,829      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 261,470,959      
Accumulated Depreciation (58,855,681)      
Investment in Real Estate, Net 202,615,278      
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 3,766,336      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2018, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 3,766,336      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 3,766,336      
Accumulated Depreciation 0      
Investment in Real Estate, Net 3,766,336      
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 14,133,106      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2018, Land 13,131,456      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 14,133,106      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 27,264,562      
Accumulated Depreciation 0      
Investment in Real Estate, Net 27,264,562      
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 1,100,410      
Gross Amount Carried at close of period 12/31/2018, Land 32,852,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 44,240,961      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 77,092,961      
Accumulated Depreciation (20,829,342)      
Investment in Real Estate, Net 56,263,619      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
660 Washington (fka Boston Common) [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 3,523,700      
Gross Amount Carried at close of period 12/31/2018, Land 106,100,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 169,835,379      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 275,935,379      
Accumulated Depreciation (41,138,920)      
Investment in Real Estate, Net 234,796,459      
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 2,269,833      
Gross Amount Carried at close of period 12/31/2018, Land 28,108,899      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 239,033,386      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 267,142,285      
Accumulated Depreciation (73,802,320)      
Investment in Real Estate, Net 193,339,965      
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 15,001,275      
Gross Amount Carried at close of period 12/31/2018, Land 22,611,600      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 92,493,446      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 115,105,046      
Accumulated Depreciation (47,229,499)      
Investment in Real Estate, Net 67,875,547      
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 443,622      
Gross Amount Carried at close of period 12/31/2018, Land 5,249,124      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 19,053,498      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 24,302,622      
Accumulated Depreciation (5,793,095)      
Investment in Real Estate, Net 18,509,527      
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 6,604,709      
Gross Amount Carried at close of period 12/31/2018, Land 27,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 175,597,149      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 203,497,149      
Accumulated Depreciation (41,358,995)      
Investment in Real Estate, Net 162,138,154      
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 4,014,061      
Gross Amount Carried at close of period 12/31/2018, Land 65,352,706      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 69,761,355      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 135,114,061      
Accumulated Depreciation (28,362,079)      
Investment in Real Estate, Net 106,751,982      
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 3,069,561      
Gross Amount Carried at close of period 12/31/2018, Land 7,786,800      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 34,656,886      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 42,443,686      
Accumulated Depreciation (10,033,292)      
Investment in Real Estate, Net 32,410,394      
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 449      
Initial Cost to Company, Land $ 41,363,921      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 280,655,909      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 32,065      
Gross Amount Carried at close of period 12/31/2018, Land 41,363,921      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 280,687,974      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 322,051,895      
Accumulated Depreciation (12,233,138)      
Investment in Real Estate, Net 309,818,757      
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 2,165,266      
Gross Amount Carried at close of period 12/31/2018, Land 5,839,548      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 31,525,718      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 37,365,266      
Accumulated Depreciation (11,163,153)      
Investment in Real Estate, Net 26,202,113      
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 303,373      
Gross Amount Carried at close of period 12/31/2018, Land 5,550,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 16,088,882      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 21,638,882      
Accumulated Depreciation (7,089,343)      
Investment in Real Estate, Net 14,549,539      
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 4,895,344      
Gross Amount Carried at close of period 12/31/2018, Land 18,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 94,689,545      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 113,589,545      
Accumulated Depreciation (22,245,031)      
Investment in Real Estate, Net 91,344,514      
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 9,293,818      
Gross Amount Carried at close of period 12/31/2018, Land 24,310,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 68,507,947      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 92,817,947      
Accumulated Depreciation (41,761,182)      
Investment in Real Estate, Net 51,056,765      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Altitude (fka Village at Howard Hughes, The (Lots 1 & 2)) [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 148,378,972      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 123,006      
Gross Amount Carried at close of period 12/31/2018, Land 43,783,485      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 148,501,978      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 192,285,463      
Accumulated Depreciation (14,509,419)      
Investment in Real Estate, Net 177,776,044      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Alton, The (fka Millikan) [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 95,898,795      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 27,038      
Gross Amount Carried at close of period 12/31/2018, Land 11,049,027      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 95,925,833      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 106,974,860      
Accumulated Depreciation (7,393,177)      
Investment in Real Estate, Net 99,581,683      
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 9,866,646      
Gross Amount Carried at close of period 12/31/2018, Land 9,057,300      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 28,350,288      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 37,407,588      
Accumulated Depreciation (16,398,864)      
Investment in Real Estate, Net 21,008,724      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
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 2,142,608      
Gross Amount Carried at close of period 12/31/2018, Land 26,650,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 64,992,608      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 91,642,608      
Accumulated Depreciation (22,783,366)      
Investment in Real Estate, Net 68,859,242      
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 2,118,504      
Gross Amount Carried at close of period 12/31/2018, Land 1,642,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 11,271,022      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 12,913,022      
Accumulated Depreciation (4,123,265)      
Investment in Real Estate, Net 8,789,757      
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 1,046,371      
Gross Amount Carried at close of period 12/31/2018, Land 8,000,400      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 37,120,971      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 45,121,371      
Accumulated Depreciation (11,684,515)      
Investment in Real Estate, Net 33,436,856      
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 267      
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 6,802,555      
Gross Amount Carried at close of period 12/31/2018, Land 12,300,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 68,268,822      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 80,568,822      
Accumulated Depreciation (17,833,191)      
Investment in Real Estate, Net 62,735,631      
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 313,737      
Gross Amount Carried at close of period 12/31/2018, Land 32,401,680      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 47,449,169      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 79,850,849      
Accumulated Depreciation (6,648,014)      
Investment in Real Estate, Net 73,202,835      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
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 18,497,683      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,876,996      
Gross Amount Carried at close of period 12/31/2018, Land 12,960,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 22,374,679      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 35,334,679      
Accumulated Depreciation (10,360,476)      
Investment in Real Estate, Net 24,974,203      
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 2,385,284      
Gross Amount Carried at close of period 12/31/2018, Land 7,995,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 20,390,284      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 28,385,284      
Accumulated Depreciation (6,758,825)      
Investment in Real Estate, Net 21,626,459      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Azure (fka Mission Bay-Block 13) [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 152,628,044      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 201,962      
Gross Amount Carried at close of period 12/31/2018, Land 32,855,115      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 152,830,006      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 185,685,121      
Accumulated Depreciation (19,304,541)      
Investment in Real Estate, Net 166,380,580      
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 3,501,456      
Gross Amount Carried at close of period 12/31/2018, Land 7,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 30,938,695      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 38,538,695      
Accumulated Depreciation (15,493,308)      
Investment in Real Estate, Net 23,045,387      
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 1,583,190      
Gross Amount Carried at close of period 12/31/2018, Land 114,351,405      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 167,231,785      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 281,583,190      
Accumulated Depreciation (46,223,187)      
Investment in Real Estate, Net 235,360,003      
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 12/31/2018, 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 (83,348)      
Investment in Real Estate, Net 218,065      
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 1,277,604      
Gross Amount Carried at close of period 12/31/2018, Land 9,098,808      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 29,978,796      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 39,077,604      
Accumulated Depreciation (8,865,592)      
Investment in Real Estate, Net 30,212,012      
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 2,103,728      
Gross Amount Carried at close of period 12/31/2018, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 75,292,990      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 75,292,990      
Accumulated Depreciation (19,870,053)      
Investment in Real Estate, Net 55,422,937      
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 4,121,529      
Gross Amount Carried at close of period 12/31/2018, Land 9,991,500      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 26,368,807      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 36,360,307      
Accumulated Depreciation (17,956,685)      
Investment in Real Estate, Net 18,403,622      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Bridford Lakes II [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 12/31/2018, 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 3,760,049      
Gross Amount Carried at close of period 12/31/2018, Land 40,099,922      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 225,198,680      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 265,298,602      
Accumulated Depreciation (61,813,037)      
Investment in Real Estate, Net 203,485,565      
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 192,535      
Gross Amount Carried at close of period 12/31/2018, Land 17,125,766      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 28,266,769      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 45,392,535      
Accumulated Depreciation (3,822,366)      
Investment in Real Estate, Net 41,570,169      
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 8,584,023      
Gross Amount Carried at close of period 12/31/2018, Land 10,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 59,951,936      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 69,951,936      
Accumulated Depreciation (32,763,420)      
Investment in Real Estate, Net 37,188,516      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
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 12,173,035      
Gross Amount Carried at close of period 12/31/2018, Land 2,288,300      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 32,769,316      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 35,057,616      
Accumulated Depreciation (27,594,760)      
Investment in Real Estate, Net 7,462,856      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Cascade [Member]        
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 148,150,309      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,109      
Gross Amount Carried at close of period 12/31/2018, Land 23,751,564      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 148,151,418      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 171,902,982      
Accumulated Depreciation (8,307,229)      
Investment in Real Estate, Net 163,595,753      
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 12,240,924      
Gross Amount Carried at close of period 12/31/2018, Land 9,700,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 82,321,302      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 92,021,302      
Accumulated Depreciation (40,391,210)      
Investment in Real Estate, Net 51,630,092      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Centre Club Combined [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 9,207,501      
Gross Amount Carried at close of period 12/31/2018, Land 7,436,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 42,222,290      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 49,658,290      
Accumulated Depreciation (24,948,636)      
Investment in Real Estate, Net 24,709,654      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Chloe [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 117      
Initial Cost to Company, Land $ 14,835,571      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 39,359,650      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 628,879      
Gross Amount Carried at close of period 12/31/2018, Land 14,835,571      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 39,988,529      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 54,824,100      
Accumulated Depreciation (2,779,352)      
Investment in Real Estate, Net 52,044,748      
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 3,104,358      
Gross Amount Carried at close of period 12/31/2018, Land 5,220,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 19,849,001      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 25,069,001      
Accumulated Depreciation (10,167,185)      
Investment in Real Estate, Net 14,901,816      
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 7,410,552      
Gross Amount Carried at close of period 12/31/2018, Land 40,400,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 103,347,598      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 143,747,598      
Accumulated Depreciation (25,436,921)      
Investment in Real Estate, Net 118,310,677      
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 2,047,704      
Gross Amount Carried at close of period 12/31/2018, Land 6,863,792      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 38,523,912      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 45,387,704      
Accumulated Depreciation (14,150,420)      
Investment in Real Estate, Net 31,237,284      
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 3,476,525      
Gross Amount Carried at close of period 12/31/2018, Land 15,100,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 45,352,782      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 60,452,782      
Accumulated Depreciation (11,624,754)      
Investment in Real Estate, Net 48,828,028      
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 13,594,830      
Gross Amount Carried at close of period 12/31/2018, Land 14,704,898      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 92,789,932      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 107,494,830      
Accumulated Depreciation (33,266,169)      
Investment in Real Estate, Net 74,228,661      
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 2,390,107      
Gross Amount Carried at close of period 12/31/2018, Land 30,400,340      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 106,214,767      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 136,615,107      
Accumulated Depreciation (33,551,922)      
Investment in Real Estate, Net 103,063,185      
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 3,945,639      
Gross Amount Carried at close of period 12/31/2018, Land 6,615,467      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 18,774,974      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 25,390,441      
Accumulated Depreciation (9,223,334)      
Investment in Real Estate, Net 16,167,107      
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 9,236,604      
Gross Amount Carried at close of period 12/31/2018, Land 27,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 123,238,899      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 150,838,899      
Accumulated Depreciation (29,100,080)      
Investment in Real Estate, Net 121,738,819      
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 1,945,268      
Gross Amount Carried at close of period 12/31/2018, Land 13,500,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 28,858,381      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 42,358,381      
Accumulated Depreciation (7,970,206)      
Investment in Real Estate, Net 34,388,175      
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 5,810,948      
Gross Amount Carried at close of period 12/31/2018, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 93,196,972      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 93,196,972      
Accumulated Depreciation (25,008,039)      
Investment in Real Estate, Net 68,188,933      
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 4,714,294      
Gross Amount Carried at close of period 12/31/2018, Land 9,606,600      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 25,907,525      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 35,514,125      
Accumulated Depreciation (17,827,109)      
Investment in Real Estate, Net 17,687,016      
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 9,986,941      
Gross Amount Carried at close of period 12/31/2018, Land 32,300,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 95,106,265      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 127,406,265      
Accumulated Depreciation (23,112,933)      
Investment in Real Estate, Net 104,293,332      
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 3,799,780      
Gross Amount Carried at close of period 12/31/2018, Land 17,200,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 51,718,755      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 68,918,755      
Accumulated Depreciation (13,497,731)      
Investment in Real Estate, Net 55,421,024      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Deerwood (SD)        
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 15,328,542      
Gross Amount Carried at close of period 12/31/2018, Land 2,082,095      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 34,068,357      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 36,150,452      
Accumulated Depreciation (29,457,997)      
Investment in Real Estate, Net 6,692,455      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Del Mar 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 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 3,997,663      
Gross Amount Carried at close of period 12/31/2018, Land 7,801,824      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 40,945,839      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 48,747,663      
Accumulated Depreciation (16,173,191)      
Investment in Real Estate, Net 32,574,472      
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 10,216,962      
Gross Amount Carried at close of period 12/31/2018, Land 1,808,900      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 26,491,323      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 28,300,223      
Accumulated Depreciation (19,595,575)      
Investment in Real Estate, Net 8,704,648      
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 1,570,420      
Gross Amount Carried at close of period 12/31/2018, Land 13,092,552      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 45,477,868      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 58,570,420      
Accumulated Depreciation (13,558,521)      
Investment in Real Estate, Net 45,011,899      
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 741,173      
Gross Amount Carried at close of period 12/31/2018, Land 14,080,560      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 57,160,613      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 71,241,173      
Accumulated Depreciation (12,317,955)      
Investment in Real Estate, Net 58,923,218      
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 31,456,250      
Gross Amount Carried at close of period 12/31/2018, Land 14,855,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 89,022,886      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 103,877,886      
Accumulated Depreciation (59,097,457)      
Investment in Real Estate, Net 44,780,429      
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 2,240,556      
Gross Amount Carried at close of period 12/31/2018, Land 8,700,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 27,686,559      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 36,386,559      
Accumulated Depreciation (9,771,700)      
Investment in Real Estate, Net 26,614,859      
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 2,547,788      
Gross Amount Carried at close of period 12/31/2018, Land 25,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 86,534,005      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 112,434,005      
Accumulated Depreciation (22,068,994)      
Investment in Real Estate, Net 90,365,011      
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 4,235,681      
Gross Amount Carried at close of period 12/31/2018, Land 25,800,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 82,988,795      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 108,788,795      
Accumulated Depreciation (21,299,475)      
Investment in Real Estate, Net 87,489,320      
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 2,905,707      
Gross Amount Carried at close of period 12/31/2018, Land 18,144,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 49,473,648      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 67,617,648      
Accumulated Depreciation (23,145,881)      
Investment in Real Estate, Net 44,471,767      
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 15,394,618      
Gross Amount Carried at close of period 12/31/2018, Land 9,209,780      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 41,117,284      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 50,327,064      
Accumulated Depreciation (24,990,335)      
Investment in Real Estate, Net 25,336,729      
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 5,447,819      
Gross Amount Carried at close of period 12/31/2018, Land 1,722,400      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 20,919,248      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 22,641,648      
Accumulated Depreciation (14,374,505)      
Investment in Real Estate, Net 8,267,143      
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 102,450,328      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 792,675      
Gross Amount Carried at close of period 12/31/2018, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 103,243,003      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 103,243,003      
Accumulated Depreciation (7,551,227)      
Investment in Real Estate, Net 95,691,776      
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 6,750,493      
Gross Amount Carried at close of period 12/31/2018, Land 10,806,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 37,085,823      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 47,891,823      
Accumulated Depreciation (18,306,144)      
Investment in Real Estate, Net 29,585,679      
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 $ 59,403,601      
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 35,187,525      
Gross Amount Carried at close of period 12/31/2018, Land 59,403,601      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 194,016,957      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 253,420,558      
Accumulated Depreciation (88,466,202)      
Investment in Real Estate, Net 164,954,356      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
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 1,757,739      
Gross Amount Carried at close of period 12/31/2018, Land 5,425,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 22,895,767      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 28,320,767      
Accumulated Depreciation (9,916,225)      
Investment in Real Estate, Net 18,404,542      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Helios (fka 2nd+Pine) [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 206,297,144      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 14,831      
Gross Amount Carried at close of period 12/31/2018, Land 18,061,674      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 206,311,975      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 224,373,649      
Accumulated Depreciation (11,942,676)      
Investment in Real Estate, Net 212,430,973      
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 2,560,256      
Gross Amount Carried at close of period 12/31/2018, Land 10,800,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 34,368,591      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 45,168,591      
Accumulated Depreciation (16,558,111)      
Investment in Real Estate, Net 28,610,480      
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 4,341,551      
Gross Amount Carried at close of period 12/31/2018, Land 6,895,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 23,325,148      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 30,220,148      
Accumulated Depreciation (10,981,639)      
Investment in Real Estate, Net 19,238,509      
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 1,045,443      
Gross Amount Carried at close of period 12/31/2018, Land 23,299,892      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 103,745,551      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 127,045,443      
Accumulated Depreciation (21,321,630)      
Investment in Real Estate, Net 105,723,813      
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 2,174,172      
Gross Amount Carried at close of period 12/31/2018, Land 10,080,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 39,701,084      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 49,781,084      
Accumulated Depreciation (18,721,344)      
Investment in Real Estate, Net 31,059,740      
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 924,031      
Gross Amount Carried at close of period 12/31/2018, Land 9,435,760      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 33,488,271      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 42,924,031      
Accumulated Depreciation (10,500,837)      
Investment in Real Estate, Net 32,423,194      
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 2,641,742      
Gross Amount Carried at close of period 12/31/2018, Land 23,420,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 72,619,441      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 96,039,441      
Accumulated Depreciation (35,972,698)      
Investment in Real Estate, Net 60,066,743      
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 6,559,255      
Gross Amount Carried at close of period 12/31/2018, Land 5,350,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 47,673,329      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 53,023,329      
Accumulated Depreciation (24,093,676)      
Investment in Real Estate, Net 28,929,653      
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 12/31/2018, 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 1,470,190      
Gross Amount Carried at close of period 12/31/2018, Land 2,732,800      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 15,358,472      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 18,091,272      
Accumulated Depreciation (7,954,981)      
Investment in Real Estate, Net 10,136,291      
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 77,708,868      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 400,967      
Gross Amount Carried at close of period 12/31/2018, Land 14,791,831      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 78,109,835      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 92,901,666      
Accumulated Depreciation (19,685,769)      
Investment in Real Estate, Net 73,215,897      
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 56,246,557      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 110,852      
Gross Amount Carried at close of period 12/31/2018, Land 11,726,305      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 56,357,409      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 68,083,714      
Accumulated Depreciation (7,480,950)      
Investment in Real Estate, Net 60,602,764      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Kelvin, The (fka Modera) [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 520,485      
Gross Amount Carried at close of period 12/31/2018, Land 15,521,552      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 65,373,933      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 80,895,485      
Accumulated Depreciation (10,153,159)      
Investment in Real Estate, Net 70,742,326      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
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 4,006,944      
Gross Amount Carried at close of period 12/31/2018, Land 14,100,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 28,669,827      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 42,769,827      
Accumulated Depreciation (13,857,402)      
Investment in Real Estate, Net 28,912,425      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
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 28,128,260      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,050,290      
Gross Amount Carried at close of period 12/31/2018, Land 13,642,420      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 33,178,550      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 46,820,970      
Accumulated Depreciation (18,704,128)      
Investment in Real Estate, Net 28,116,842      
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 12,850,243      
Gross Amount Carried at close of period 12/31/2018, Land 27,246,045      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 50,591,293      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 77,837,338      
Accumulated Depreciation (31,145,964)      
Investment in Real Estate, Net 46,691,374      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
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 2,105,715      
Gross Amount Carried at close of period 12/31/2018, Land 16,382,822      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 85,922,793      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 102,305,615      
Accumulated Depreciation (28,986,710)      
Investment in Real Estate, Net 73,318,905      
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 14,626,711      
Gross Amount Carried at close of period 12/31/2018, Land 5,928,400      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 48,221,973      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 54,150,373      
Accumulated Depreciation (36,031,322)      
Investment in Real Estate, Net 18,119,051      
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 1,577,513      
Gross Amount Carried at close of period 12/31/2018, Land 5,805,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 27,282,513      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 33,087,513      
Accumulated Depreciation (9,306,827)      
Investment in Real Estate, Net 23,780,686      
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 732,963      
Gross Amount Carried at close of period 12/31/2018, Land 20,100,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 68,641,986      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 88,741,986      
Accumulated Depreciation (16,094,383)      
Investment in Real Estate, Net 72,647,603      
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 6,554,452      
Gross Amount Carried at close of period 12/31/2018, Land 18,696,674      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 85,000,109      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 103,696,783      
Accumulated Depreciation (20,874,720)      
Investment in Real Estate, Net 82,822,063      
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 3,845,833      
Gross Amount Carried at close of period 12/31/2018, Land 73,170,045      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 57,808,343      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 130,978,388      
Accumulated Depreciation (24,364,056)      
Investment in Real Estate, Net 106,614,332      
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 $ 38,264,917      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 132,175,915      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 82,037,087      
Gross Amount Carried at close of period 12/31/2018, Land 38,264,917      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 214,213,002      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 252,477,919      
Accumulated Depreciation (143,886,095)      
Investment in Real Estate, Net 108,591,824      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
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 7,188,625      
Gross Amount Carried at close of period 12/31/2018, Land 20,880,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 97,444,134      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 118,324,134      
Accumulated Depreciation (45,368,039)      
Investment in Real Estate, Net 72,956,095      
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 942,456      
Gross Amount Carried at close of period 12/31/2018, Land 22,346,513      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 62,443,614      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 84,790,127      
Accumulated Depreciation (15,923,495)      
Investment in Real Estate, Net 68,866,632      
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 8,397,509      
Gross Amount Carried at close of period 12/31/2018, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 177,239,951      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 177,239,951      
Accumulated Depreciation (47,146,998)      
Investment in Real Estate, Net 130,092,953      
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 5,580,206      
Gross Amount Carried at close of period 12/31/2018, Land 60,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 94,891,688      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 155,791,688      
Accumulated Depreciation (24,699,526)      
Investment in Real Estate, Net 131,092,162      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
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 2,328,664      
Gross Amount Carried at close of period 12/31/2018, Land 13,740,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 43,085,965      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 56,825,965      
Accumulated Depreciation (19,556,103)      
Investment in Real Estate, Net 37,269,862      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
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 2,362,369      
Gross Amount Carried at close of period 12/31/2018, Land 8,540,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 14,572,350      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 23,112,350      
Accumulated Depreciation (6,573,840)      
Investment in Real Estate, Net 16,538,510      
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 2,883,991      
Gross Amount Carried at close of period 12/31/2018, Land 8,125,216      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 30,262,775      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 38,387,991      
Accumulated Depreciation (8,050,414)      
Investment in Real Estate, Net 30,337,577      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
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 8,205,107      
Gross Amount Carried at close of period 12/31/2018, Land 8,160,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 37,566,045      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 45,726,045      
Accumulated Depreciation (25,291,041)      
Investment in Real Estate, Net 20,435,004      
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 1,270,920      
Gross Amount Carried at close of period 12/31/2018, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 60,851,818      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 60,851,818      
Accumulated Depreciation (21,513,518)      
Investment in Real Estate, Net 39,338,300      
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 160,996      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2018, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 160,996      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 160,996      
Accumulated Depreciation 0      
Investment in Real Estate, Net 160,996      
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 2,384,578      
Gross Amount Carried at close of period 12/31/2018, Land 8,500,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 54,914,024      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 63,414,024      
Accumulated Depreciation (24,082,672)      
Investment in Real Estate, Net 39,331,352      
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 9,551,107      
Gross Amount Carried at close of period 12/31/2018, Land 75,800,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 112,256,508      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 188,056,508      
Accumulated Depreciation (30,064,769)      
Investment in Real Estate, Net 157,991,739      
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 4,743,836      
Gross Amount Carried at close of period 12/31/2018, Land 4,000,159      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 99,034,426      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 103,034,585      
Accumulated Depreciation (49,673,731)      
Investment in Real Estate, Net 53,360,854      
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 5,764,419      
Gross Amount Carried at close of period 12/31/2018, Land 9,360,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 26,542,972      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 35,902,972      
Accumulated Depreciation (15,274,806)      
Investment in Real Estate, Net 20,628,166      
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 14,751,585      
Gross Amount Carried at close of period 12/31/2018, Land 38,607,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 92,223,802      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 130,830,802      
Accumulated Depreciation (36,348,320)      
Investment in Real Estate, Net 94,482,482      
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 11,428,402      
Gross Amount Carried at close of period 12/31/2018, Land 5,524,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 26,120,107      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 31,644,107      
Accumulated Depreciation (19,830,954)      
Investment in Real Estate, Net 11,813,153      
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 10,707,930      
Gross Amount Carried at close of period 12/31/2018, Land 3,390,700      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 41,225,204      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 44,615,904      
Accumulated Depreciation (31,925,485)      
Investment in Real Estate, Net 12,690,419      
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 6,184,215      
Gross Amount Carried at close of period 12/31/2018, Land 23,400,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 67,204,653      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 90,604,653      
Accumulated Depreciation (36,500,570)      
Investment in Real Estate, Net 54,104,083      
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 4,071,719      
Gross Amount Carried at close of period 12/31/2018, Land 15,400,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 39,546,055      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 54,946,055      
Accumulated Depreciation (10,060,766)      
Investment in Real Estate, Net 44,885,289      
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 4,523,128      
Gross Amount Carried at close of period 12/31/2018, Land 5,111,200      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 16,433,566      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 21,544,766      
Accumulated Depreciation (11,149,744)      
Investment in Real Estate, Net 10,395,022      
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 63,651,394      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 43,186      
Gross Amount Carried at close of period 12/31/2018, Land 16,807,519      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 63,694,580      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 80,502,099      
Accumulated Depreciation (8,420,800)      
Investment in Real Estate, Net 72,081,299      
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 802,966      
Gross Amount Carried at close of period 12/31/2018, Land 7,740,467      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 44,949,147      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 52,689,614      
Accumulated Depreciation (6,895,004)      
Investment in Real Estate, Net 45,794,610      
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 138,212,568      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 10,366      
Gross Amount Carried at close of period 12/31/2018, Land 30,224,393      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 138,222,934      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 168,447,327      
Accumulated Depreciation (10,939,933)      
Investment in Real Estate, Net 157,507,394      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
One India Street (fka 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 3,346,235      
Gross Amount Carried at close of period 12/31/2018, Land 22,200,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 32,019,214      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 54,219,214      
Accumulated Depreciation (8,203,480)      
Investment in Real Estate, Net 46,015,734      
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 1,796,632      
Gross Amount Carried at close of period 12/31/2018, Land 32,250,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 112,546,632      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 144,796,632      
Accumulated Depreciation (27,949,911)      
Investment in Real Estate, Net 116,846,721      
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 691,363      
Gross Amount Carried at close of period 12/31/2018, Land 5,911,041      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 20,646,322      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 26,557,363      
Accumulated Depreciation (3,017,526)      
Investment in Real Estate, Net 23,539,837      
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 6,345,232      
Gross Amount Carried at close of period 12/31/2018, Land 40,504,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 24,370,911      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 64,874,911      
Accumulated Depreciation (13,224,242)      
Investment in Real Estate, Net 51,650,669      
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 7,488,875      
Gross Amount Carried at close of period 12/31/2018, Land 37,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 17,344,472      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 54,944,472      
Accumulated Depreciation (11,104,877)      
Investment in Real Estate, Net 43,839,595      
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 9,179,112      
Gross Amount Carried at close of period 12/31/2018, Land 52,654,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 32,224,863      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 84,878,863      
Accumulated Depreciation (18,199,716)      
Investment in Real Estate, Net 66,679,147      
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 10,892,394      
Gross Amount Carried at close of period 12/31/2018, Land 102,163,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 119,881,796      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 222,044,796      
Accumulated Depreciation (52,426,236)      
Investment in Real Estate, Net 169,618,560      
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 65,073,509      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 212,580      
Gross Amount Carried at close of period 12/31/2018, Land 16,667,059      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 65,286,089      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 81,953,148      
Accumulated Depreciation (9,333,810)      
Investment in Real Estate, Net 72,619,338      
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 2,436,695      
Gross Amount Carried at close of period 12/31/2018, Land 28,300,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 81,274,879      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 109,574,879      
Accumulated Depreciation (20,074,236)      
Investment in Real Estate, Net 89,500,643      
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 1,663,394      
Gross Amount Carried at close of period 12/31/2018, Land 13,700,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 60,750,913      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 74,450,913      
Accumulated Depreciation (14,438,751)      
Investment in Real Estate, Net 60,012,162      
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 4,858,184      
Gross Amount Carried at close of period 12/31/2018, Land 43,200,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 133,611,543      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 176,811,543      
Accumulated Depreciation (34,884,871)      
Investment in Real Estate, Net 141,926,672      
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 11,262,203      
Gross Amount Carried at close of period 12/31/2018, Land 3,033,500      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 38,564,586      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 41,598,086      
Accumulated Depreciation (29,343,622)      
Investment in Real Estate, Net 12,254,464      
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 7,163,451      
Gross Amount Carried at close of period 12/31/2018, Land 6,246,700      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 18,990,904      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 25,237,604      
Accumulated Depreciation (12,327,804)      
Investment in Real Estate, Net 12,909,800      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Pearl, The (WA) [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 999,509      
Gross Amount Carried at close of period 12/31/2018, Land 6,972,585      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 27,526,924      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 34,499,509      
Accumulated Depreciation (3,981,489)      
Investment in Real Estate, Net 30,518,020      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Pearl MDR (fka 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 4,778,318      
Gross Amount Carried at close of period 12/31/2018, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 125,573,677      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 125,573,677      
Accumulated Depreciation (33,800,305)      
Investment in Real Estate, Net 91,773,372      
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 6,080,345      
Gross Amount Carried at close of period 12/31/2018, Land 18,094,052      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 87,986,293      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 106,080,345      
Accumulated Depreciation (29,282,736)      
Investment in Real Estate, Net 76,797,609      
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 23,015,281      
Gross Amount Carried at close of period 12/31/2018, Land 35,100,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 56,489,103      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 91,589,103      
Accumulated Depreciation (28,347,617)      
Investment in Real Estate, Net 63,241,486      
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 3,777,392      
Gross Amount Carried at close of period 12/31/2018, Land 3,572,400      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 18,438,386      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 22,010,786      
Accumulated Depreciation (13,473,788)      
Investment in Real Estate, Net 8,536,998      
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 5,637,028      
Gross Amount Carried at close of period 12/31/2018, Land 8,640,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 27,124,154      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 35,764,154      
Accumulated Depreciation (16,434,227)      
Investment in Real Estate, Net 19,329,927      
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 23,175,339      
Gross Amount Carried at close of period 12/31/2018, Land 22,487,006      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 120,018,252      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 142,505,258      
Accumulated Depreciation (84,850,599)      
Investment in Real Estate, Net 57,654,659      
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 179,509,834      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 120,105      
Gross Amount Carried at close of period 12/31/2018, Land 40,830,011      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 179,629,939      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 220,459,950      
Accumulated Depreciation (18,869,635)      
Investment in Real Estate, Net 201,590,315      
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 4,453,741      
Gross Amount Carried at close of period 12/31/2018, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 72,431,054      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 72,431,054      
Accumulated Depreciation (18,216,430)      
Investment in Real Estate, Net 54,214,624      
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 273      
Initial Cost to Company, Land $ 34,625,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 77,879,740      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,499,005      
Gross Amount Carried at close of period 12/31/2018, Land 34,625,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 79,378,745      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 114,003,745      
Accumulated Depreciation (30,036,655)      
Investment in Real Estate, Net 83,967,090      
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 171,558,177      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 127,665      
Gross Amount Carried at close of period 12/31/2018, Land 76,292,169      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 171,685,842      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 247,978,011      
Accumulated Depreciation (25,554,087)      
Investment in Real Estate, Net 222,423,924      
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 9,741,254      
Gross Amount Carried at close of period 12/31/2018, Land 28,200,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 79,537,169      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 107,737,169      
Accumulated Depreciation (41,393,133)      
Investment in Real Estate, Net 66,344,036      
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 3,095,294      
Gross Amount Carried at close of period 12/31/2018, Land 3,573,621      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 22,150,799      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 25,724,420      
Accumulated Depreciation (11,070,038)      
Investment in Real Estate, Net 14,654,382      
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 2,829,890      
Gross Amount Carried at close of period 12/31/2018, Land 26,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 87,241,052      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 114,141,052      
Accumulated Depreciation (22,257,122)      
Investment in Real Estate, Net 91,883,930      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Radius Uptown [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Denver, CO      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 372      
Initial Cost to Company, Land $ 13,644,960      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 121,899,032      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 93,774      
Gross Amount Carried at close of period 12/31/2018, Land 13,644,960      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 121,992,806      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 135,637,766      
Accumulated Depreciation (3,902,658)      
Investment in Real Estate, Net 131,735,108      
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 1,306,822      
Gross Amount Carried at close of period 12/31/2018, Land 15,546,376      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 66,626,832      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 82,173,208      
Accumulated Depreciation (18,309,824)      
Investment in Real Estate, Net 63,863,384      
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 1,106,972      
Gross Amount Carried at close of period 12/31/2018, Land 10,300,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 34,595,717      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 44,895,717      
Accumulated Depreciation (9,833,862)      
Investment in Real Estate, Net 35,061,855      
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 6,506,417      
Gross Amount Carried at close of period 12/31/2018, Land 1,857,400      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 23,219,671      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 25,077,071      
Accumulated Depreciation (18,325,451)      
Investment in Real Estate, Net 6,751,620      
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 200,843      
Gross Amount Carried at close of period 12/31/2018, Land 2,458,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 4,742,843      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 7,200,843      
Accumulated Depreciation (2,002,770)      
Investment in Real Estate, Net 5,198,073      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
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 4,759,258      
Gross Amount Carried at close of period 12/31/2018, Land 10,500,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 57,572,193      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 68,072,193      
Accumulated Depreciation (30,673,683)      
Investment in Real Estate, Net 37,398,510      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
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 4,515,799      
Gross Amount Carried at close of period 12/31/2018, Land 6,500,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 39,100,859      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 45,600,859      
Accumulated Depreciation (20,712,491)      
Investment in Real Estate, Net 24,888,368      
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 3,320,031      
Gross Amount Carried at close of period 12/31/2018, Land 16,345,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 76,400,701      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 92,745,701      
Accumulated Depreciation (36,394,123)      
Investment in Real Estate, Net 56,351,578      
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 7,621,478      
Gross Amount Carried at close of period 12/31/2018, Land 27,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 40,651,083      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 67,651,083      
Accumulated Depreciation (10,869,571)      
Investment in Real Estate, Net 56,781,512      
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 15,256,457      
Gross Amount Carried at close of period 12/31/2018, Land 11,918,917      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 84,119,098      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 96,038,015      
Accumulated Depreciation (42,003,388)      
Investment in Real Estate, Net 54,034,627      
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 5,623,360      
Gross Amount Carried at close of period 12/31/2018, Land 16,768,705      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 83,134,883      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 99,903,588      
Accumulated Depreciation (33,572,969)      
Investment in Real Estate, Net 66,330,619      
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 109,259,858      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 353,398      
Gross Amount Carried at close of period 12/31/2018, Land 17,859,785      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 109,613,256      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 127,473,041      
Accumulated Depreciation (22,357,191)      
Investment in Real Estate, Net 105,115,850      
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 40,449,028      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 60,085      
Gross Amount Carried at close of period 12/31/2018, Land 12,118,248      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 40,509,113      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 52,627,361      
Accumulated Depreciation (5,850,705)      
Investment in Real Estate, Net 46,776,656      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Rianna I & 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 156      
Initial Cost to Company, Land $ 4,430,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 29,298,096      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,133,335      
Gross Amount Carried at close of period 12/31/2018, Land 4,430,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 30,431,431      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 34,861,431      
Accumulated Depreciation (11,522,763)      
Investment in Real Estate, Net 23,338,668      
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 5,830,811      
Gross Amount Carried at close of period 12/31/2018, Land 11,809,500      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 39,834,859      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 51,644,359      
Accumulated Depreciation (26,215,341)      
Investment in Real Estate, Net 25,429,018      
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 4,579,233      
Gross Amount Carried at close of period 12/31/2018, Land 34,963,355      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 89,166,891      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 124,130,246      
Accumulated Depreciation (23,808,487)      
Investment in Real Estate, Net 100,321,759      
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 2,273,237      
Gross Amount Carried at close of period 12/31/2018, Land 17,136,645      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 42,809,768      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 59,946,413      
Accumulated Depreciation (10,623,659)      
Investment in Real Estate, Net 49,322,754      
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 3,905,450      
Gross Amount Carried at close of period 12/31/2018, Land 14,355,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 84,799,499      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 99,154,499      
Accumulated Depreciation (24,557,962)      
Investment in Real Estate, Net 74,596,537      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Rivington, The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Hoboken, NJ      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 240      
Initial Cost to Company, Land $ 34,340,640      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 112,110,289      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 524,731      
Gross Amount Carried at close of period 12/31/2018, Land 34,340,640      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 112,635,020      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 146,975,660      
Accumulated Depreciation (6,937,992)      
Investment in Real Estate, Net 140,037,668      
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 1,342,588      
Gross Amount Carried at close of period 12/31/2018, Land 4,922,840      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 31,544,748      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 36,467,588      
Accumulated Depreciation (10,069,250)      
Investment in Real Estate, Net 26,398,338      
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 1,440,822      
Gross Amount Carried at close of period 12/31/2018, Land 14,641,990      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 44,298,832      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 58,940,822      
Accumulated Depreciation (14,646,231)      
Investment in Real Estate, Net 44,294,591      
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 4,466,962      
Gross Amount Carried at close of period 12/31/2018, Land 663,800      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 10,441,765      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 11,105,565      
Accumulated Depreciation (7,764,932)      
Investment in Real Estate, Net 3,340,633      
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 15,840,921      
Gross Amount Carried at close of period 12/31/2018, Land 3,342,381      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 47,178,253      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 50,520,634      
Accumulated Depreciation (37,713,141)      
Investment in Real Estate, Net 12,807,493      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
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 7,343,477      
Gross Amount Carried at close of period 12/31/2018, Land 8,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 31,426,501      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 40,326,501      
Accumulated Depreciation (21,400,131)      
Investment in Real Estate, Net 18,926,370      
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 5,774,667      
Gross Amount Carried at close of period 12/31/2018, Land 10,560,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 31,349,124      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 41,909,124      
Accumulated Depreciation (18,371,799)      
Investment in Real Estate, Net 23,537,325      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Skyhouse Denver [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Denver, CO      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 354      
Initial Cost to Company, Land $ 13,562,331      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 126,360,129      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 98,231      
Gross Amount Carried at close of period 12/31/2018, Land 13,562,331      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 126,458,360      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 140,020,691      
Accumulated Depreciation (3,622,426)      
Investment in Real Estate, Net 136,398,265      
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 5,618,577      
Gross Amount Carried at close of period 12/31/2018, Land 1,781,600      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 22,350,493      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 24,132,093      
Accumulated Depreciation (14,414,952)      
Investment in Real Estate, Net 9,717,141      
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 8,156,471      
Gross Amount Carried at close of period 12/31/2018, Land 16,836,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 43,570,471      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 60,406,471      
Accumulated Depreciation (15,013,850)      
Investment in Real Estate, Net 45,392,621      
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 45,016,303      
Gross Amount Carried at close of period 12/31/2018, Land 78,278,200      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 136,501,894      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 214,780,094      
Accumulated Depreciation (77,594,870)      
Investment in Real Estate, Net 137,185,224      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
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 5,500,993      
Gross Amount Carried at close of period 12/31/2018, Land 3,380,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 27,453,856      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 30,833,856      
Accumulated Depreciation (17,769,582)      
Investment in Real Estate, Net 13,064,274      
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 5,741,605      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2018, Land 29,406,606      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 5,741,605      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 35,148,211      
Accumulated Depreciation 0      
Investment in Real Estate, Net 35,148,211      
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 6,018,250      
Gross Amount Carried at close of period 12/31/2018, Land 7,503,400      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 30,066,757      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 37,570,157      
Accumulated Depreciation (19,961,454)      
Investment in Real Estate, Net 17,608,703      
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 368      
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 4,611,766      
Gross Amount Carried at close of period 12/31/2018, Land 68,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 84,088,627      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 152,988,627      
Accumulated Depreciation (21,524,365)      
Investment in Real Estate, Net 131,464,262      
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 6,760,016      
Gross Amount Carried at close of period 12/31/2018, Land 6,936,600      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 21,084,085      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 28,020,685      
Accumulated Depreciation (12,852,392)      
Investment in Real Estate, Net 15,168,293      
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 1,145,000      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2018, Land 18,200,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 1,145,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 19,345,000      
Accumulated Depreciation 0      
Investment in Real Estate, Net 19,345,000      
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 $ 9,163,667      
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 390,699      
Gross Amount Carried at close of period 12/31/2018, Land 9,163,667      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 48,301,680      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 57,465,347      
Accumulated Depreciation (4,533,798)      
Investment in Real Estate, Net 52,931,549      
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 12/31/2018, 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 9,140,862      
Gross Amount Carried at close of period 12/31/2018, Land 26,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 37,575,886      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 63,575,886      
Accumulated Depreciation (11,439,522)      
Investment in Real Estate, Net 52,136,364      
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 337,851      
Gross Amount Carried at close of period 12/31/2018, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 59,219,724      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 59,219,724      
Accumulated Depreciation (14,245,570)      
Investment in Real Estate, Net 44,974,154      
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 1,758,321      
Gross Amount Carried at close of period 12/31/2018, Land 14,087,610      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 18,072,472      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 32,160,082      
Accumulated Depreciation (6,415,798)      
Investment in Real Estate, Net 25,744,284      
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 7,870,443      
Gross Amount Carried at close of period 12/31/2018, Land 26,767,171      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 226,693,171      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 253,460,342      
Accumulated Depreciation (78,218,773)      
Investment in Real Estate, Net 175,241,569      
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 756,472      
Gross Amount Carried at close of period 12/31/2018, Land 7,030,766      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 29,762,234      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 36,793,000      
Accumulated Depreciation (6,893,992)      
Investment in Real Estate, Net 29,899,008      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
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 20,588,732      
Gross Amount Carried at close of period 12/31/2018, Land 39,410,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 71,394,804      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 110,804,804      
Accumulated Depreciation (40,974,164)      
Investment in Real Estate, Net 69,830,640      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
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 8,490,378      
Gross Amount Carried at close of period 12/31/2018, Land 24,360,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 94,669,092      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 119,029,092      
Accumulated Depreciation (44,377,201)      
Investment in Real Estate, Net 74,651,891      
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 4,433,417      
Gross Amount Carried at close of period 12/31/2018, Land 15,568,464      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 59,463,024      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 75,031,488      
Accumulated Depreciation (21,151,199)      
Investment in Real Estate, Net 53,880,289      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Troy 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 378      
Initial Cost to Company, Land $ 34,641,051      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 181,602,575      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 101,573      
Gross Amount Carried at close of period 12/31/2018, Land 34,641,051      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 181,704,148      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 216,345,199      
Accumulated Depreciation (6,623,226)      
Investment in Real Estate, Net 209,721,973      
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 75,800,090      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,262,298      
Gross Amount Carried at close of period 12/31/2018, Land 12,542,418      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 77,062,388      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 89,604,806      
Accumulated Depreciation (17,836,404)      
Investment in Real Estate, Net 71,768,402      
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 2,039,013      
Gross Amount Carried at close of period 12/31/2018, Land 8,800,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 24,227,301      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 33,027,301      
Accumulated Depreciation (11,748,837)      
Investment in Real Estate, Net 21,278,464      
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 10,163,129      
Gross Amount Carried at close of period 12/31/2018, Land 9,403,960      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 200,759,169      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 210,163,129      
Accumulated Depreciation (66,454,004)      
Investment in Real Estate, Net 143,709,125      
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 1,429,925      
Gross Amount Carried at close of period 12/31/2018, Land 15,322,724      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 77,606,519      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 92,929,243      
Accumulated Depreciation (20,521,554)      
Investment in Real Estate, Net 72,407,689      
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 4,455,624      
Gross Amount Carried at close of period 12/31/2018, Land 5,190,700      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 14,134,733      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 19,325,433      
Accumulated Depreciation (10,358,163)      
Investment in Real Estate, Net 8,967,270      
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 3,510,354      
Gross Amount Carried at close of period 12/31/2018, Land 18,539,817      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 133,917,719      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 152,457,536      
Accumulated Depreciation (43,822,971)      
Investment in Real Estate, Net 108,634,565      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
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 1,665,109      
Gross Amount Carried at close of period 12/31/2018, Land 10,590,975      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 46,074,134      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 56,665,109      
Accumulated Depreciation (17,179,349)      
Investment in Real Estate, Net 39,485,760      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
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 1,003,076      
Gross Amount Carried at close of period 12/31/2018, Land 10,350,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 36,436,513      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 46,786,513      
Accumulated Depreciation (15,908,114)      
Investment in Real Estate, Net 30,878,399      
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 10,741,608      
Gross Amount Carried at close of period 12/31/2018, Land 1,665,100      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 25,727,286      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 27,392,386      
Accumulated Depreciation (20,635,508)      
Investment in Real Estate, Net 6,756,878      
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 1,925,886      
Gross Amount Carried at close of period 12/31/2018, Land 15,100,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 42,785,282      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 57,885,282      
Accumulated Depreciation (11,360,058)      
Investment in Real Estate, Net 46,525,224      
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 1,539,555      
Gross Amount Carried at close of period 12/31/2018, Land 7,059,230      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 49,217,317      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 56,276,547      
Accumulated Depreciation (21,895,611)      
Investment in Real Estate, Net 34,380,936      
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 5,670,439      
Gross Amount Carried at close of period 12/31/2018, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 91,610,442      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 91,610,442      
Accumulated Depreciation (22,371,237)      
Investment in Real Estate, Net 69,239,205      
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 176,040,861      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 230,941      
Gross Amount Carried at close of period 12/31/2018, Land 27,709,329      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 176,271,802      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 203,981,131      
Accumulated Depreciation (19,667,441)      
Investment in Real Estate, Net 184,313,690      
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 17,318,936      
Gross Amount Carried at close of period 12/31/2018, Land 4,525,800      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 58,055,229      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 62,581,029      
Accumulated Depreciation (48,290,527)      
Investment in Real Estate, Net 14,290,502      
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 2,389,563      
Gross Amount Carried at close of period 12/31/2018, Land 15,550,260      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 71,839,303      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 87,389,563      
Accumulated Depreciation (25,840,645)      
Investment in Real Estate, Net 61,548,918      
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 4,411,295      
Gross Amount Carried at close of period 12/31/2018, Land 12,448,888      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 56,455,743      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 68,904,631      
Accumulated Depreciation (19,527,545)      
Investment in Real Estate, Net 49,377,086      
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 10,053,790      
Gross Amount Carried at close of period 12/31/2018, Land 34,400,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 118,539,649      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 152,939,649      
Accumulated Depreciation (30,280,723)      
Investment in Real Estate, Net 122,658,926      
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 1,559,270      
Gross Amount Carried at close of period 12/31/2018, Land 16,800,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 35,633,326      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 52,433,326      
Accumulated Depreciation (8,944,170)      
Investment in Real Estate, Net 43,489,156      
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 5,705,814      
Gross Amount Carried at close of period 12/31/2018, Land 84,800,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 72,761,316      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 157,561,316      
Accumulated Depreciation (20,616,675)      
Investment in Real Estate, Net 136,944,641      
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 3,668,190      
Gross Amount Carried at close of period 12/31/2018, Land 469,546      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 166,791,212      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 167,260,758      
Accumulated Depreciation (61,427,741)      
Investment in Real Estate, Net 105,833,017      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
West End Tower (fka 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 $ 10,424,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 38,294,331      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2018, Land 10,424,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 38,294,331      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 48,718,331      
Accumulated Depreciation 0      
Investment in Real Estate, Net 48,718,331      
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 884,695      
Gross Amount Carried at close of period 12/31/2018, Land 10,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 45,019,902      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 55,619,902      
Accumulated Depreciation (11,209,736)      
Investment in Real Estate, Net 44,410,166      
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 4,398,852      
Gross Amount Carried at close of period 12/31/2018, Land 64,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 65,542,111      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 130,442,111      
Accumulated Depreciation (16,741,081)      
Investment in Real Estate, Net 113,701,030      
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 3,066,088      
Gross Amount Carried at close of period 12/31/2018, Land 34,200,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 60,028,718      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 94,228,718      
Accumulated Depreciation (14,822,757)      
Investment in Real Estate, Net 79,405,961      
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 1,111,261      
Gross Amount Carried at close of period 12/31/2018, Land 3,060,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 6,650,132      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 9,710,132      
Accumulated Depreciation (3,887,667)      
Investment in Real Estate, Net 5,822,465      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Westside Barry (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 648,119      
Gross Amount Carried at close of period 12/31/2018, Land 1,530,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 3,671,642      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 5,201,642      
Accumulated Depreciation (2,196,161)      
Investment in Real Estate, Net 3,005,481      
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 736,265      
Gross Amount Carried at close of period 12/31/2018, Land 1,785,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 3,969,519      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 5,754,519      
Accumulated Depreciation (2,392,392)      
Investment in Real Estate, Net 3,362,127      
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 660,089      
Gross Amount Carried at close of period 12/31/2018, Land 1,955,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 4,201,524      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 6,156,524      
Accumulated Depreciation (2,501,347)      
Investment in Real Estate, Net 3,655,177      
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 1,003,468      
Gross Amount Carried at close of period 12/31/2018, Land 3,060,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 6,542,858      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 9,602,858      
Accumulated Depreciation (3,890,635)      
Investment in Real Estate, Net 5,712,223      
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 2,720,073      
Gross Amount Carried at close of period 12/31/2018, Land 9,605,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 22,703,458      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 32,308,458      
Accumulated Depreciation (13,177,962)      
Investment in Real Estate, Net 19,130,496      
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 12,358,198      
Gross Amount Carried at close of period 12/31/2018, Land 2,662,900      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 36,343,695      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 39,006,595      
Accumulated Depreciation (27,568,039)      
Investment in Real Estate, Net 11,438,556      
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 9,340,814      
Gross Amount Carried at close of period 12/31/2018, Land 9,729,900      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 32,350,582      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 42,080,482      
Accumulated Depreciation (23,075,720)      
Investment in Real Estate, Net 19,004,762      
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 117,010,784      
Gross Amount Carried at close of period 12/31/2018, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 117,010,784      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 117,010,784      
Accumulated Depreciation (96,891,265)      
Investment in Real Estate, Net 20,119,519      
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 10,278,996      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2018, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 10,278,996      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 10,278,996      
Accumulated Depreciation 0      
Investment in Real Estate, Net 10,278,996      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Other [Member]        
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 74,341      
Gross Amount Carried at close of period 12/31/2018, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 74,341      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 74,341      
Accumulated Depreciation (29,979)      
Investment in Real Estate, Net 44,362      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Wholly Owned Unencumbered [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Units | ApartmentUnit 62,862      
Initial Cost to Company, Land $ 4,900,861,387      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 15,320,429,009      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,387,840,336      
Gross Amount Carried at close of period 12/31/2018, Land 4,900,861,387      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 16,708,269,345      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 21,609,130,732      
Accumulated Depreciation (5,400,484,879)      
Investment in Real Estate, Net 16,208,645,853      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
1401 Joyce on Pentagon Row [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 5,209,262      
Gross Amount Carried at close of period 12/31/2018, Land 9,780,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 94,877,427      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 104,657,427      
Accumulated Depreciation (34,814,020)      
Investment in Real Estate, Net 69,843,407      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 57,384,106      
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 6,617,637      
Gross Amount Carried at close of period 12/31/2018, Land 13,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 81,888,816      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 94,888,816      
Accumulated Depreciation (20,177,043)      
Investment in Real Estate, Net $ 74,711,773      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
300 East 39th (fka 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 4,927,499      
Gross Amount Carried at close of period 12/31/2018, Land 48,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 101,102,138      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 150,002,138      
Accumulated Depreciation (25,417,391)      
Investment in Real Estate, Net 124,584,747      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 61,139,469      
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 6,389,689      
Gross Amount Carried at close of period 12/31/2018, Land 79,400,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 85,512,313      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 164,912,313      
Accumulated Depreciation (22,235,813)      
Investment in Real Estate, Net $ 142,676,500      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
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 3,606,786      
Gross Amount Carried at close of period 12/31/2018, Land 12,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 38,001,558      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 50,601,558      
Accumulated Depreciation (9,639,353)      
Investment in Real Estate, Net $ 40,962,205      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
55 West Fifth I & II (fka Townhouse Plaza and Gardens) [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 13,082,237      
Gross Amount Carried at close of period 12/31/2018, Land 21,041,710      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 85,013,560      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 106,055,270      
Accumulated Depreciation (25,342,170)      
Investment in Real Estate, Net 80,713,100      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 25,456,082      
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 2,551,093      
Gross Amount Carried at close of period 12/31/2018, Land 59,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 158,412,698      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 218,312,698      
Accumulated Depreciation (38,237,590)      
Investment in Real Estate, Net 180,075,108      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 78,599,339      
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 7,292,188      
Gross Amount Carried at close of period 12/31/2018, Land 3,252,993      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 29,037,783      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 32,290,776      
Accumulated Depreciation (18,665,226)      
Investment in Real Estate, Net 13,625,550      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 119,684      
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 8,913,532      
Gross Amount Carried at close of period 12/31/2018, Land 25,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 32,506,726      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 57,506,726      
Accumulated Depreciation (19,215,717)      
Investment in Real Estate, Net 38,291,009      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 19,985,389      
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 1,103,680      
Gross Amount Carried at close of period 12/31/2018, Land 11,379,497      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 50,464,183      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 61,843,680      
Accumulated Depreciation (9,767,220)      
Investment in Real Estate, Net 52,076,460      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 27,756,919      
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 1,670,956      
Gross Amount Carried at close of period 12/31/2018, Land 7,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 22,208,315      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 29,208,315      
Accumulated Depreciation (12,312,121)      
Investment in Real Estate, Net 16,896,194      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 22,766,586      
Avenir Apartments [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 114,321,619      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,484,463      
Gross Amount Carried at close of period 12/31/2018, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 117,806,082      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 117,806,082      
Accumulated Depreciation (28,125,723)      
Investment in Real Estate, Net 89,680,359      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 87,221,511      
Bella Vista I, II, III Combined [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 8,186,190      
Gross Amount Carried at close of period 12/31/2018, Land 31,682,754      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 129,281,976      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 160,964,730      
Accumulated Depreciation (58,472,749)      
Investment in Real Estate, Net 102,491,981      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 57,966,537      
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 673,901      
Gross Amount Carried at close of period 12/31/2018, Land 4,377,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 16,696,011      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 21,073,011      
Accumulated Depreciation (7,235,667)      
Investment in Real Estate, Net 13,837,344      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 8,100,556      
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 2,208,011      
Gross Amount Carried at close of period 12/31/2018, Land 12,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 45,735,390      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 58,335,390      
Accumulated Depreciation (11,663,122)      
Investment in Real Estate, Net $ 46,672,268      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
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 2,730,568      
Gross Amount Carried at close of period 12/31/2018, Land 3,397,100      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 12,019,642      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 15,416,742      
Accumulated Depreciation (8,256,357)      
Investment in Real Estate, Net 7,160,385      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 9,234,049      
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 2,094,969      
Gross Amount Carried at close of period 12/31/2018, Land 9,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 19,045,295      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 28,045,295      
Accumulated Depreciation (4,826,188)      
Investment in Real Estate, Net $ 23,219,107      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
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 4,858,254      
Gross Amount Carried at close of period 12/31/2018, Land 18,300,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 71,250,668      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 89,550,668      
Accumulated Depreciation (17,799,363)      
Investment in Real Estate, Net $ 71,751,305      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
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 2,877,507      
Gross Amount Carried at close of period 12/31/2018, Land 23,500,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 55,922,580      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 79,422,580      
Accumulated Depreciation (14,794,273)      
Investment in Real Estate, Net $ 64,628,307      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
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 1,657,294      
Gross Amount Carried at close of period 12/31/2018, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 125,417,098      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 125,417,098      
Accumulated Depreciation (32,083,921)      
Investment in Real Estate, Net $ 93,333,177      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
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 1,210,925      
Gross Amount Carried at close of period 12/31/2018, Land 23,500,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 88,933,246      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 112,433,246      
Accumulated Depreciation (21,595,734)      
Investment in Real Estate, Net $ 90,837,512      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
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 8,602,359      
Gross Amount Carried at close of period 12/31/2018, Land 6,510,200      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 48,292,479      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 54,802,679      
Accumulated Depreciation (34,338,783)      
Investment in Real Estate, Net 20,463,896      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 31,348,151      
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 880,966      
Gross Amount Carried at close of period 12/31/2018, Land 7,817,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 27,343,738      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 35,160,738      
Accumulated Depreciation (11,703,908)      
Investment in Real Estate, Net 23,456,830      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 15,772,690      
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 3,179,209      
Gross Amount Carried at close of period 12/31/2018, Land 35,200,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 111,947,407      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 147,147,407      
Accumulated Depreciation (25,978,612)      
Investment in Real Estate, Net $ 121,168,795      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
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 400,152      
Gross Amount Carried at close of period 12/31/2018, Land 7,113,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 26,023,978      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 33,136,978      
Accumulated Depreciation (11,264,581)      
Investment in Real Estate, Net 21,872,397      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 14,310,309      
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 1,136,625      
Gross Amount Carried at close of period 12/31/2018, Land 17,500,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 75,815,542      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 93,315,542      
Accumulated Depreciation (17,882,838)      
Investment in Real Estate, Net 75,432,704      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 94,150,066      
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 3,425,049      
Gross Amount Carried at close of period 12/31/2018, Land 16,047,022      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 52,076,012      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 68,123,034      
Accumulated Depreciation (15,990,887)      
Investment in Real Estate, Net 52,132,147      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 32,199,417      
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 10,753,054      
Gross Amount Carried at close of period 12/31/2018, Land 2,512,500      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 33,364,966      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 35,877,466      
Accumulated Depreciation (25,621,271)      
Investment in Real Estate, Net 10,256,195      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 46,495,108      
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 656,460      
Gross Amount Carried at close of period 12/31/2018, Land 10,752,145      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 35,284,575      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 46,036,720      
Accumulated Depreciation (13,177,993)      
Investment in Real Estate, Net 32,858,727      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 26,234,062      
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 2,304,807      
Gross Amount Carried at close of period 12/31/2018, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 43,555,851      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 43,555,851      
Accumulated Depreciation (18,264,493)      
Investment in Real Estate, Net 25,291,358      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 24,997,955      
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 6,765,782      
Gross Amount Carried at close of period 12/31/2018, Land 5,977,504      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 33,514,893      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 39,492,397      
Accumulated Depreciation (18,532,044)      
Investment in Real Estate, Net 20,960,353      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 24,966,238      
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 14,775,239      
Gross Amount Carried at close of period 12/31/2018, Land 12,858,693      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 71,943,742      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 84,802,435      
Accumulated Depreciation (36,507,386)      
Investment in Real Estate, Net 48,295,049      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 69,282,256      
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 1,379,251      
Gross Amount Carried at close of period 12/31/2018, Land 12,649,228      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 38,221,263      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 50,870,491      
Accumulated Depreciation (13,657,076)      
Investment in Real Estate, Net $ 37,213,415      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
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 9,447,968      
Gross Amount Carried at close of period 12/31/2018, Land 14,752,034      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 82,783,393      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 97,535,427      
Accumulated Depreciation (43,130,107)      
Investment in Real Estate, Net 54,405,320      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 49,823,673      
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 13,040,037      
Gross Amount Carried at close of period 12/31/2018, Land 71,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 224,947,178      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 296,847,178      
Accumulated Depreciation (56,244,011)      
Investment in Real Estate, Net $ 240,603,167      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
Reserve at Fairfax Corner [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 11,739,962      
Gross Amount Carried at close of period 12/31/2018, Land 15,804,057      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 74,869,013      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 90,673,070      
Accumulated Depreciation (41,689,916)      
Investment in Real Estate, Net 48,983,154      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 84,717,832      
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 12,766,992      
Gross Amount Carried at close of period 12/31/2018, Land 79,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 190,083,969      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 269,983,969      
Accumulated Depreciation (45,375,257)      
Investment in Real Estate, Net $ 224,608,712      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
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 74,562      
Gross Amount Carried at close of period 12/31/2018, Land 7,222,544      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 26,352,018      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 33,574,562      
Accumulated Depreciation (5,408,769)      
Investment in Real Estate, Net $ 28,165,793      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
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 8,181,014      
Gross Amount Carried at close of period 12/31/2018, Land 2,629,804      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 31,851,903      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 34,481,707      
Accumulated Depreciation (23,765,883)      
Investment in Real Estate, Net 10,715,824      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 38,020,343      
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 6,795,448      
Gross Amount Carried at close of period 12/31/2018, Land 28,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 68,712,118      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 97,312,118      
Accumulated Depreciation (31,806,076)      
Investment in Real Estate, Net 65,506,042      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 37,940,000      
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 199,965      
Gross Amount Carried at close of period 12/31/2018, Land 2,736,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 8,009,992      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 10,745,992      
Accumulated Depreciation (3,570,951)      
Investment in Real Estate, Net 7,175,041      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 4,874,236      
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 1,203,271      
Gross Amount Carried at close of period 12/31/2018, Land 42,580,326      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 57,217,945      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 99,798,271      
Accumulated Depreciation (10,415,693)      
Investment in Real Estate, Net 89,382,578      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 40,501,067      
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 7,510,844      
Gross Amount Carried at close of period 12/31/2018, Land 12,650,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 41,167,136      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 53,817,136      
Accumulated Depreciation (22,859,119)      
Investment in Real Estate, Net 30,958,017      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 30,357,682      
Vintage at 425 Broadway (fka Promenade) [Memebr]        
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 1,763,696      
Gross Amount Carried at close of period 12/31/2018, Land 9,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 15,725,219      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 24,725,219      
Accumulated Depreciation (4,182,605)      
Investment in Real Estate, Net $ 20,542,614      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
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 3,801,228      
Gross Amount Carried at close of period 12/31/2018, Land 60,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 51,995,065      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 112,895,065      
Accumulated Depreciation (14,869,327)      
Investment in Real Estate, Net 98,025,738      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 48,175,896      
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 133,467,158      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,575,071      
Gross Amount Carried at close of period 12/31/2018, Land 22,898,848      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 136,042,229      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 158,941,077      
Accumulated Depreciation (37,281,584)      
Investment in Real Estate, Net 121,659,493      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 96,386,296      
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 5,181,298      
Gross Amount Carried at close of period 12/31/2018, Land 8,550,600      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 22,169,481      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 30,720,081      
Accumulated Depreciation (15,240,849)      
Investment in Real Estate, Net 15,479,232      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 17,835,169      
Portfolio/Entity Encumbrances [Member]        
Real Estate And Accumulated Depreciation Abstract        
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 0      
Gross Amount Carried at close of period 12/31/2018, Land 0      
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 0      
Accumulated Depreciation 0      
Investment in Real Estate, Net 0      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 797,768,476      
Investment in Real Estate - Wholly Owned Encumbered [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Units | ApartmentUnit 12,140      
Initial Cost to Company, Land $ 932,672,559      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 2,860,557,660      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 229,886,950      
Gross Amount Carried at close of period 12/31/2018, Land 932,672,559      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 3,090,444,610      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 4,023,117,169      
Accumulated Depreciation (1,039,436,780)      
Investment in Real Estate, Net 2,983,680,389      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 2,081,887,149      
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 6,928,668      
Gross Amount Carried at close of period 12/31/2018, Land 796,800      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 14,102,393      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 14,899,193      
Accumulated Depreciation (11,358,634)      
Investment in Real Estate, Net 3,540,559      
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 4,016,206      
Gross Amount Carried at close of period 12/31/2018, Land 4,869,448      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 15,971,270      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 20,840,718      
Accumulated Depreciation (11,185,103)      
Investment in Real Estate, Net 9,655,615      
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 6,941,477      
Gross Amount Carried at close of period 12/31/2018, Land 6,105,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 36,503,342      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 42,608,342      
Accumulated Depreciation (21,079,355)      
Investment in Real Estate, Net 21,528,987      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Harrison Square (fka Elliot Bay) [Member]        
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 5,487,099      
Gross Amount Carried at close of period 12/31/2018, Land 7,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 41,331,444      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 48,931,444      
Accumulated Depreciation (11,150,395)      
Investment in Real Estate, Net 37,781,049      
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 224,059      
Gross Amount Carried at close of period 12/31/2018, Land 32,494,154      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 84,869,261      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 117,363,415      
Accumulated Depreciation (8,194,532)      
Investment in Real Estate, Net 109,168,883      
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 3,822,519      
Gross Amount Carried at close of period 12/31/2018, Land 5,460,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 19,544,089      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 25,004,089      
Accumulated Depreciation (13,068,617)      
Investment in Real Estate, Net 11,935,472      
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 966,107      
Gross Amount Carried at close of period 12/31/2018, Land 4,400,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 13,934,109      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 18,334,109      
Accumulated Depreciation (6,624,197)      
Investment in Real Estate, Net 11,709,912      
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 151,652,048      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 160,761      
Gross Amount Carried at close of period 12/31/2018, Land 26,626,498      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 151,812,809      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 178,439,307      
Accumulated Depreciation (10,307,620)      
Investment in Real Estate, Net 168,131,687      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Wood Creek II (fka Willow Brook (CA)) [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 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 6,854,946      
Gross Amount Carried at close of period 12/31/2018, Land 5,055,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 45,243,618      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 50,298,618      
Accumulated Depreciation (23,768,126)      
Investment in Real Estate, Net 26,530,492      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Partially Owned Unencumbered [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Units | ApartmentUnit 1,847      
Initial Cost to Company, Land $ 93,406,900      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 387,910,493      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 35,401,842      
Gross Amount Carried at close of period 12/31/2018, Land 93,406,900      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 423,312,335      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 516,719,235      
Accumulated Depreciation (116,736,579)      
Investment in Real Estate, Net 399,982,656      
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 5,634,209      
Gross Amount Carried at close of period 12/31/2018, Land 4,507,100      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 18,209,023      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 22,716,123      
Accumulated Depreciation (13,322,710)      
Investment in Real Estate, Net 9,393,413      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 16,515,951      
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 18,812,121      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,726,619      
Gross Amount Carried at close of period 12/31/2018, Land 5,425,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 26,538,740      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 31,963,740      
Accumulated Depreciation (17,263,363)      
Investment in Real Estate, Net 14,700,377      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 28,150,731      
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 6,896,605      
Gross Amount Carried at close of period 12/31/2018, Land 6,945,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 29,961,581      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 36,906,581      
Accumulated Depreciation (18,556,525)      
Investment in Real Estate, Net 18,350,056      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 36,425,025      
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 5,636,468      
Gross Amount Carried at close of period 12/31/2018, Land 5,345,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 26,027,086      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 31,372,086      
Accumulated Depreciation (16,017,984)      
Investment in Real Estate, Net 15,354,102      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 28,839,869      
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 5,074,751      
Gross Amount Carried at close of period 12/31/2018, Land 4,550,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 23,139,515      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 27,689,515      
Accumulated Depreciation (14,268,541)      
Investment in Real Estate, Net 13,420,974      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 26,144,881      
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 3,347,614      
Gross Amount Carried at close of period 12/31/2018, Land 3,057,100      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 11,196,232      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 14,253,332      
Accumulated Depreciation (7,873,885)      
Investment in Real Estate, Net 6,379,447      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 9,819,750      
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 3,070,140      
Gross Amount Carried at close of period 12/31/2018, Land 5,500,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 18,286,753      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 23,786,753      
Accumulated Depreciation (9,309,905)      
Investment in Real Estate, Net 14,476,848      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 9,885,805      
Wisconsin Place [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 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 1,277,053      
Gross Amount Carried at close of period 12/31/2018, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 173,366,408      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 173,366,408      
Accumulated Depreciation (43,009,588)      
Investment in Real Estate, Net 130,356,820      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 147,801,323      
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 288,061,879      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 38,663,459      
Gross Amount Carried at close of period 12/31/2018, Land 35,329,200      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 326,725,338      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 362,054,538      
Accumulated Depreciation (139,622,501)      
Investment in Real Estate, Net 222,432,037      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 303,583,335      
Total Consolidated Investment in Real Estate [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Units | ApartmentUnit 78,537      
Initial Cost to Company, Land $ 5,962,270,046      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 18,856,959,041      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,691,792,587      
Gross Amount Carried at close of period 12/31/2018, Land 5,962,270,046      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 20,548,751,628      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 26,511,021,674      
Accumulated Depreciation (6,696,280,739)      
Investment in Real Estate, Net 19,814,740,935      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 2,385,470,484