XML 85 R72.htm IDEA: XBRL DOCUMENT v3.4.0.3
SCHEDULE III - REAL ESTATE AND ACCUMULATED DEPRECIATION (Details) - USD ($)
 12 Months Ended
Apr. 30, 2015
Apr. 30, 2014
Apr. 30, 2013
Apr. 30, 2015
Apr. 30, 2014
Apr. 30, 2013
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       $ 667,544,000    
Initial Cost to Company [Abstract]            
Land       146,965,000    
Buildings & Improvements       1,349,531,000    
Costs capitalized subsequent to acquisition       229,692,000    
Gross amount at which carried at close of period [Abstract]            
Land       167,129,000    
Buildings & Improvements       1,559,059,000    
Total $ 1,726,189,000     1,726,189,000    
Accumulated Depreciation $ (313,308,000)     (313,308,000)    
Maximum borrowing capacity       90,000,000    
Advances under the facility specified as percentage of value of properties provided as security (in hundredths) 60.00%          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,726,189,000          
Deductions during year [Abstract]            
Balance at close of year 313,308,000          
Total real estate investments [2]       1,412,880,000 $ 1,275,284,000 $ 1,214,235,000
Net basis of real estate investments for federal income tax purposes       1,700,000,000 1,500,000,000 1,500,000,000
Minimum [Member]            
Gross amount at which carried at close of period [Abstract]            
Maximum borrowing capacity       90,000,000    
Maximum [Member]            
Gross amount at which carried at close of period [Abstract]            
Maximum borrowing capacity       100,000,000    
Discontinued Operations [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       295,678,000    
Initial Cost to Company [Abstract]            
Land       76,228,000    
Buildings & Improvements       405,130,000    
Costs capitalized subsequent to acquisition       70,311,000    
Gross amount at which carried at close of period [Abstract]            
Land       80,424,000    
Buildings & Improvements       471,245,000    
Total 551,669,000     551,669,000    
Accumulated Depreciation (135,679,000)     (135,679,000)    
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year 551,669,000          
Deductions during year [Abstract]            
Balance at close of year 135,679,000          
Discontinued Operations [Member] | 610 Business Center IV - Brooklyn Park, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       6,759,000    
Initial Cost to Company [Abstract]            
Land       975,000    
Buildings & Improvements       5,542,000    
Costs capitalized subsequent to acquisition       2,886,000    
Gross amount at which carried at close of period [Abstract]            
Land       980,000    
Buildings & Improvements       8,423,000    
Total 9,403,000     9,403,000    
Accumulated Depreciation $ (2,408,000)     (2,408,000)    
Date of Construction or Acquisition 2007          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 9,403,000          
Deductions during year [Abstract]            
Balance at close of year 2,408,000          
Discontinued Operations [Member] | 7800 West Brown Deer Road - Milwaukee, WI [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       10,320,000    
Initial Cost to Company [Abstract]            
Land       1,455,000    
Buildings & Improvements       8,756,000    
Costs capitalized subsequent to acquisition       2,431,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,475,000    
Buildings & Improvements       11,167,000    
Total 12,642,000     12,642,000    
Accumulated Depreciation $ (4,022,000)     (4,022,000)    
Date of Construction or Acquisition 2003          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 12,642,000          
Deductions during year [Abstract]            
Balance at close of year 4,022,000          
Discontinued Operations [Member] | American Corporate Center - Mendota Heights, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       8,670,000    
Initial Cost to Company [Abstract]            
Land       893,000    
Buildings & Improvements       16,768,000    
Costs capitalized subsequent to acquisition       4,067,000    
Gross amount at which carried at close of period [Abstract]            
Land       893,000    
Buildings & Improvements       20,835,000    
Total 21,728,000     21,728,000    
Accumulated Depreciation $ (8,926,000)     (8,926,000)    
Date of Construction or Acquisition 2002          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 21,728,000          
Deductions during year [Abstract]            
Balance at close of year 8,926,000          
Discontinued Operations [Member] | Ameritrade - Omaha, NE [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       2,020,000    
Initial Cost to Company [Abstract]            
Land       327,000    
Buildings & Improvements       7,957,000    
Costs capitalized subsequent to acquisition       65,000    
Gross amount at which carried at close of period [Abstract]            
Land       327,000    
Buildings & Improvements       8,022,000    
Total 8,349,000     8,349,000    
Accumulated Depreciation $ (3,215,000)     (3,215,000)    
Date of Construction or Acquisition 1999          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 8,349,000          
Deductions during year [Abstract]            
Balance at close of year 3,215,000          
Discontinued Operations [Member] | Benton Business Park - Sauk Rapids, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       0    
Initial Cost to Company [Abstract]            
Land       188,000    
Buildings & Improvements       1,261,000    
Costs capitalized subsequent to acquisition       87,000    
Gross amount at which carried at close of period [Abstract]            
Land       188,000    
Buildings & Improvements       1,348,000    
Total 1,536,000     1,536,000    
Accumulated Depreciation $ (429,000)     (429,000)    
Date of Construction or Acquisition 2003          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,536,000          
Deductions during year [Abstract]            
Balance at close of year 429,000          
Discontinued Operations [Member] | Brenwood - Minnetonka, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       0    
Initial Cost to Company [Abstract]            
Land       1,642,000    
Buildings & Improvements       12,138,000    
Costs capitalized subsequent to acquisition       3,864,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,650,000    
Buildings & Improvements       15,994,000    
Total 17,644,000     17,644,000    
Accumulated Depreciation $ (5,810,000)     (5,810,000)    
Date of Construction or Acquisition 2002          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 17,644,000          
Deductions during year [Abstract]            
Balance at close of year 5,810,000          
Discontinued Operations [Member] | Brook Valley I - La Vista, NE [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       1,209,000    
Initial Cost to Company [Abstract]            
Land       347,000    
Buildings & Improvements       1,671,000    
Costs capitalized subsequent to acquisition       134,000    
Gross amount at which carried at close of period [Abstract]            
Land       347,000    
Buildings & Improvements       1,805,000    
Total 2,152,000     2,152,000    
Accumulated Depreciation $ (458,000)     (458,000)    
Date of Construction or Acquisition 2005          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 2,152,000          
Deductions during year [Abstract]            
Balance at close of year 458,000          
Discontinued Operations [Member] | Corporate Center West - Omaha, NE [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       17,315,000    
Initial Cost to Company [Abstract]            
Land       3,880,000    
Buildings & Improvements       5,253,000    
Costs capitalized subsequent to acquisition       21,000    
Gross amount at which carried at close of period [Abstract]            
Land       3,880,000    
Buildings & Improvements       5,274,000    
Total 9,154,000     9,154,000    
Accumulated Depreciation $ (126,000)     (126,000)    
Date of Construction or Acquisition 2006          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 9,154,000          
Deductions during year [Abstract]            
Balance at close of year 126,000          
Discontinued Operations [Member] | Crosstown Centre - Eden Prairie, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       9,000,000    
Initial Cost to Company [Abstract]            
Land       2,884,000    
Buildings & Improvements       14,569,000    
Costs capitalized subsequent to acquisition       3,183,000    
Gross amount at which carried at close of period [Abstract]            
Land       2,980,000    
Buildings & Improvements       17,656,000    
Total 20,636,000     20,636,000    
Accumulated Depreciation $ (4,939,000)     (4,939,000)    
Date of Construction or Acquisition 2004          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 20,636,000          
Deductions during year [Abstract]            
Balance at close of year 4,939,000          
Discontinued Operations [Member] | Eden Prairie 6101 Blue Circle Dr - Eden Prairie [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       0    
Initial Cost to Company [Abstract]            
Land       666,000    
Buildings & Improvements       4,197,000    
Costs capitalized subsequent to acquisition       1,000    
Gross amount at which carried at close of period [Abstract]            
Land       666,000    
Buildings & Improvements       4,198,000    
Total 4,864,000     4,864,000    
Accumulated Depreciation $ (1,701,000)     (1,701,000)    
Date of Construction or Acquisition 1999          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 4,864,000          
Deductions during year [Abstract]            
Balance at close of year 1,701,000          
Discontinued Operations [Member] | Farnam Executive Center - Omaha, NE [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       12,160,000    
Initial Cost to Company [Abstract]            
Land       2,188,000    
Buildings & Improvements       7,912,000    
Costs capitalized subsequent to acquisition       1,000    
Gross amount at which carried at close of period [Abstract]            
Land       2,188,000    
Buildings & Improvements       7,913,000    
Total 10,101,000     10,101,000    
Accumulated Depreciation $ (190,000)     (190,000)    
Date of Construction or Acquisition 2006          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 10,101,000          
Deductions during year [Abstract]            
Balance at close of year 190,000          
Discontinued Operations [Member] | Flagship - Eden Prairie, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       21,565,000    
Initial Cost to Company [Abstract]            
Land       1,899,000    
Buildings & Improvements       15,518,000    
Costs capitalized subsequent to acquisition       31,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,913,000    
Buildings & Improvements       15,535,000    
Total 17,448,000     17,448,000    
Accumulated Depreciation $ (373,000)     (373,000)    
Date of Construction or Acquisition 2006          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 17,448,000          
Deductions during year [Abstract]            
Balance at close of year 373,000          
Discontinued Operations [Member] | Gateway Corporate Center - Woodbury, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       8,700,000    
Initial Cost to Company [Abstract]            
Land       1,637,000    
Buildings & Improvements       6,663,000    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       1,637,000    
Buildings & Improvements       6,663,000    
Total 8,300,000     8,300,000    
Accumulated Depreciation $ (160,000)     (160,000)    
Date of Construction or Acquisition 2006          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 8,300,000          
Deductions during year [Abstract]            
Balance at close of year 160,000          
Discontinued Operations [Member] | Golden Hills Office Center - Golden Valley, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       17,417,000    
Initial Cost to Company [Abstract]            
Land       3,018,000    
Buildings & Improvements       18,544,000    
Costs capitalized subsequent to acquisition       4,313,000    
Gross amount at which carried at close of period [Abstract]            
Land       3,018,000    
Buildings & Improvements       22,857,000    
Total 25,875,000     25,875,000    
Accumulated Depreciation $ (8,851,000)     (8,851,000)    
Date of Construction or Acquisition 2003          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 25,875,000          
Deductions during year [Abstract]            
Balance at close of year 8,851,000          
Discontinued Operations [Member] | Granite Corporate Center - St. Cloud, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       5,313,000    
Initial Cost to Company [Abstract]            
Land       588,000    
Buildings & Improvements       7,808,000    
Costs capitalized subsequent to acquisition       1,521,000    
Gross amount at which carried at close of period [Abstract]            
Land       740,000    
Buildings & Improvements       9,177,000    
Total 9,917,000     9,917,000    
Accumulated Depreciation $ (3,524,000)     (3,524,000)    
Date of Construction or Acquisition 2001          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 9,917,000          
Deductions during year [Abstract]            
Balance at close of year 3,524,000          
Discontinued Operations [Member] | Great Plains - Fargo, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       0    
Initial Cost to Company [Abstract]            
Land       126,000    
Buildings & Improvements       15,240,000    
Costs capitalized subsequent to acquisition       721,000    
Gross amount at which carried at close of period [Abstract]            
Land       126,000    
Buildings & Improvements       15,961,000    
Total 16,087,000     16,087,000    
Accumulated Depreciation $ (6,161,000)     (6,161,000)    
Date of Construction or Acquisition 1997          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 16,087,000          
Deductions during year [Abstract]            
Balance at close of year 6,161,000          
Discontinued Operations [Member] | Highlands Ranch I - Highlands Ranch, CO [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       0    
Initial Cost to Company [Abstract]            
Land       2,268,000    
Buildings & Improvements       8,362,000    
Costs capitalized subsequent to acquisition       1,117,000    
Gross amount at which carried at close of period [Abstract]            
Land       2,268,000    
Buildings & Improvements       9,479,000    
Total 11,747,000     11,747,000    
Accumulated Depreciation $ (2,211,000)     (2,211,000)    
Date of Construction or Acquisition 2006          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 11,747,000          
Deductions during year [Abstract]            
Balance at close of year 2,211,000          
Discontinued Operations [Member] | Highlands Ranch II - Highlands Ranch, CO [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       0    
Initial Cost to Company [Abstract]            
Land       1,437,000    
Buildings & Improvements       9,549,000    
Costs capitalized subsequent to acquisition       1,901,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,437,000    
Buildings & Improvements       11,450,000    
Total 12,887,000     12,887,000    
Accumulated Depreciation $ (3,391,000)     (3,391,000)    
Date of Construction or Acquisition 2004          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 12,887,000          
Deductions during year [Abstract]            
Balance at close of year 3,391,000          
Discontinued Operations [Member] | Interlachen Corporate Center - Edina, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       8,800,000    
Initial Cost to Company [Abstract]            
Land       1,650,000    
Buildings & Improvements       14,983,000    
Costs capitalized subsequent to acquisition       2,530,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,693,000    
Buildings & Improvements       17,470,000    
Total 19,163,000     19,163,000    
Accumulated Depreciation $ (6,389,000)     (6,389,000)    
Date of Construction or Acquisition 2001          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 19,163,000          
Deductions during year [Abstract]            
Balance at close of year 6,389,000          
Discontinued Operations [Member] | Intertech Building - Fenton, MO [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       4,177,000    
Initial Cost to Company [Abstract]            
Land       2,130,000    
Buildings & Improvements       3,968,000    
Costs capitalized subsequent to acquisition       1,721,000    
Gross amount at which carried at close of period [Abstract]            
Land       2,191,000    
Buildings & Improvements       5,628,000    
Total 7,819,000     7,819,000    
Accumulated Depreciation $ (1,253,000)     (1,253,000)    
Date of Construction or Acquisition 2007          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 7,819,000          
Deductions during year [Abstract]            
Balance at close of year 1,253,000          
Discontinued Operations [Member] | Mendota Office Center I - Mendota Heights, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       3,734,000    
Initial Cost to Company [Abstract]            
Land       835,000    
Buildings & Improvements       6,169,000    
Costs capitalized subsequent to acquisition       1,402,000    
Gross amount at which carried at close of period [Abstract]            
Land       835,000    
Buildings & Improvements       7,571,000    
Total 8,406,000     8,406,000    
Accumulated Depreciation $ (2,683,000)     (2,683,000)    
Date of Construction or Acquisition 2002          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 8,406,000          
Deductions during year [Abstract]            
Balance at close of year 2,683,000          
Discontinued Operations [Member] | Mendota Office Center II - Mendota Heights, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       5,516,000    
Initial Cost to Company [Abstract]            
Land       1,121,000    
Buildings & Improvements       10,085,000    
Costs capitalized subsequent to acquisition       2,097,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,121,000    
Buildings & Improvements       12,182,000    
Total 13,303,000     13,303,000    
Accumulated Depreciation $ (4,882,000)     (4,882,000)    
Date of Construction or Acquisition 2002          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 13,303,000          
Deductions during year [Abstract]            
Balance at close of year 4,882,000          
Discontinued Operations [Member] | Mendota Office Center III - Mendota Heights, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       3,791,000    
Initial Cost to Company [Abstract]            
Land       970,000    
Buildings & Improvements       5,734,000    
Costs capitalized subsequent to acquisition       957,000    
Gross amount at which carried at close of period [Abstract]            
Land       970,000    
Buildings & Improvements       6,691,000    
Total 7,661,000     7,661,000    
Accumulated Depreciation $ (2,419,000)     (2,419,000)    
Date of Construction or Acquisition 2002          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 7,661,000          
Deductions during year [Abstract]            
Balance at close of year 2,419,000          
Discontinued Operations [Member] | Mendota Office Center IV - Mendota Heights, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       4,507,000    
Initial Cost to Company [Abstract]            
Land       1,070,000    
Buildings & Improvements       7,635,000    
Costs capitalized subsequent to acquisition       1,510,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,070,000    
Buildings & Improvements       9,145,000    
Total 10,215,000     10,215,000    
Accumulated Depreciation $ (3,235,000)     (3,235,000)    
Date of Construction or Acquisition 2002          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 10,215,000          
Deductions during year [Abstract]            
Balance at close of year 3,235,000          
Discontinued Operations [Member] | Minnesota National Bank - Duluth, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       628,000    
Initial Cost to Company [Abstract]            
Land       287,000    
Buildings & Improvements       1,454,000    
Costs capitalized subsequent to acquisition       224,000    
Gross amount at which carried at close of period [Abstract]            
Land       288,000    
Buildings & Improvements       1,677,000    
Total 1,965,000     1,965,000    
Accumulated Depreciation $ (475,000)     (475,000)    
Date of Construction or Acquisition 2004          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,965,000          
Deductions during year [Abstract]            
Balance at close of year 475,000          
Discontinued Operations [Member] | Miracle Hills One - Omaha, NE [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       8,895,000    
Initial Cost to Company [Abstract]            
Land       1,974,000    
Buildings & Improvements       5,726,000    
Costs capitalized subsequent to acquisition       6,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,974,000    
Buildings & Improvements       5,732,000    
Total 7,706,000     7,706,000    
Accumulated Depreciation $ (139,000)     (139,000)    
Date of Construction or Acquisition 2006          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 7,706,000          
Deductions during year [Abstract]            
Balance at close of year 139,000          
Discontinued Operations [Member] | Northpark Corporate Center - Arden Hills, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       11,519,000    
Initial Cost to Company [Abstract]            
Land       2,034,000    
Buildings & Improvements       14,584,000    
Costs capitalized subsequent to acquisition       2,497,000    
Gross amount at which carried at close of period [Abstract]            
Land       2,037,000    
Buildings & Improvements       17,078,000    
Total 19,115,000     19,115,000    
Accumulated Depreciation $ (4,231,000)     (4,231,000)    
Date of Construction or Acquisition 2006          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 19,115,000          
Deductions during year [Abstract]            
Balance at close of year 4,231,000          
Discontinued Operations [Member] | Omaha 10802 Farnam Dr - Omaha, NE [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       5,061,000    
Initial Cost to Company [Abstract]            
Land       2,462,000    
Buildings & Improvements       4,374,000    
Costs capitalized subsequent to acquisition       392,000    
Gross amount at which carried at close of period [Abstract]            
Land       2,818,000    
Buildings & Improvements       4,410,000    
Total 7,228,000     7,228,000    
Accumulated Depreciation $ (525,000)     (525,000)    
Date of Construction or Acquisition 2010          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 7,228,000          
Deductions during year [Abstract]            
Balance at close of year 525,000          
Discontinued Operations [Member] | Pacific Hills - Omaha, NE [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       16,770,000    
Initial Cost to Company [Abstract]            
Land       4,220,000    
Buildings & Improvements       6,280,000    
Costs capitalized subsequent to acquisition       243,000    
Gross amount at which carried at close of period [Abstract]            
Land       4,220,000    
Buildings & Improvements       6,523,000    
Total 10,743,000     10,743,000    
Accumulated Depreciation $ (180,000)     (180,000)    
Date of Construction or Acquisition 2006          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 10,743,000          
Deductions during year [Abstract]            
Balance at close of year 180,000          
Discontinued Operations [Member] | Plaza VII - Boise, ID [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       0    
Initial Cost to Company [Abstract]            
Land       300,000    
Buildings & Improvements       913,000    
Costs capitalized subsequent to acquisition       4,000    
Gross amount at which carried at close of period [Abstract]            
Land       300,000    
Buildings & Improvements       917,000    
Total 1,217,000     1,217,000    
Accumulated Depreciation $ (11,000)     (11,000)    
Date of Construction or Acquisition 2003          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,217,000          
Deductions during year [Abstract]            
Balance at close of year 11,000          
Discontinued Operations [Member] | Plymouth 5095 Nathan Lane - Plymouth, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       1,147,000    
Initial Cost to Company [Abstract]            
Land       604,000    
Buildings & Improvements       1,253,000    
Costs capitalized subsequent to acquisition       87,000    
Gross amount at which carried at close of period [Abstract]            
Land       636,000    
Buildings & Improvements       1,308,000    
Total 1,944,000     1,944,000    
Accumulated Depreciation $ (258,000)     (258,000)    
Date of Construction or Acquisition 2007          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,944,000          
Deductions during year [Abstract]            
Balance at close of year 258,000          
Discontinued Operations [Member] | Prairie Oak Business Center - Eden Prairie, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       3,120,000    
Initial Cost to Company [Abstract]            
Land       531,000    
Buildings & Improvements       4,069,000    
Costs capitalized subsequent to acquisition       2,523,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,030,000    
Buildings & Improvements       6,093,000    
Total 7,123,000     7,123,000    
Accumulated Depreciation $ (2,365,000)     (2,365,000)    
Date of Construction or Acquisition 2003          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 7,123,000          
Deductions during year [Abstract]            
Balance at close of year 2,365,000          
Discontinued Operations [Member] | Rapid City 900 Concourse Drive - Rapid City, SD [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       181,000    
Initial Cost to Company [Abstract]            
Land       285,000    
Buildings & Improvements       6,600,000    
Costs capitalized subsequent to acquisition       1,151,000    
Gross amount at which carried at close of period [Abstract]            
Land       514,000    
Buildings & Improvements       7,522,000    
Total 8,036,000     8,036,000    
Accumulated Depreciation $ (2,912,000)     (2,912,000)    
Date of Construction or Acquisition 2000          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 8,036,000          
Deductions during year [Abstract]            
Balance at close of year 2,912,000          
Discontinued Operations [Member] | Riverport - Maryland Heights, MO [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       19,690,000    
Initial Cost to Company [Abstract]            
Land       1,891,000    
Buildings & Improvements       6,109,000    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       1,891,000    
Buildings & Improvements       6,109,000    
Total 8,000,000     8,000,000    
Accumulated Depreciation $ (146,000)     (146,000)    
Date of Construction or Acquisition 2006          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 8,000,000          
Deductions during year [Abstract]            
Balance at close of year 146,000          
Discontinued Operations [Member] | Spring Valley IV - Omaha, NE [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       720,000    
Initial Cost to Company [Abstract]            
Land       178,000    
Buildings & Improvements       916,000    
Costs capitalized subsequent to acquisition       60,000    
Gross amount at which carried at close of period [Abstract]            
Land       186,000    
Buildings & Improvements       968,000    
Total 1,154,000     1,154,000    
Accumulated Depreciation $ (259,000)     (259,000)    
Date of Construction or Acquisition 2005          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,154,000          
Deductions during year [Abstract]            
Balance at close of year 259,000          
Discontinued Operations [Member] | Spring Valley V - Omaha, NE [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       792,000    
Initial Cost to Company [Abstract]            
Land       212,000    
Buildings & Improvements       1,123,000    
Costs capitalized subsequent to acquisition       251,000    
Gross amount at which carried at close of period [Abstract]            
Land       240,000    
Buildings & Improvements       1,346,000    
Total 1,586,000     1,586,000    
Accumulated Depreciation $ (388,000)     (388,000)    
Date of Construction or Acquisition 2005          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,586,000          
Deductions during year [Abstract]            
Balance at close of year 388,000          
Discontinued Operations [Member] | Spring Valley X - Omaha, NE [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       734,000    
Initial Cost to Company [Abstract]            
Land       180,000    
Buildings & Improvements       1,024,000    
Costs capitalized subsequent to acquisition       80,000    
Gross amount at which carried at close of period [Abstract]            
Land       189,000    
Buildings & Improvements       1,095,000    
Total 1,284,000     1,284,000    
Accumulated Depreciation $ (282,000)     (282,000)    
Date of Construction or Acquisition 2005          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,284,000          
Deductions during year [Abstract]            
Balance at close of year 282,000          
Discontinued Operations [Member] | Spring Valley XI - Omaha, NE [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       720,000    
Initial Cost to Company [Abstract]            
Land       143,000    
Buildings & Improvements       1,094,000    
Costs capitalized subsequent to acquisition       36,000    
Gross amount at which carried at close of period [Abstract]            
Land       151,000    
Buildings & Improvements       1,122,000    
Total 1,273,000     1,273,000    
Accumulated Depreciation $ (276,000)     (276,000)    
Date of Construction or Acquisition 2005          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,273,000          
Deductions during year [Abstract]            
Balance at close of year 276,000          
Discontinued Operations [Member] | Superior Office Building - Duluth, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       944,000    
Initial Cost to Company [Abstract]            
Land       336,000    
Buildings & Improvements       2,200,000    
Costs capitalized subsequent to acquisition       143,000    
Gross amount at which carried at close of period [Abstract]            
Land       336,000    
Buildings & Improvements       2,343,000    
Total 2,679,000     2,679,000    
Accumulated Depreciation $ (688,000)     (688,000)    
Date of Construction or Acquisition 2004          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 2,679,000          
Deductions during year [Abstract]            
Balance at close of year 688,000          
Discontinued Operations [Member] | TCA Building - Eagan, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       7,500,000    
Initial Cost to Company [Abstract]            
Land       627,000    
Buildings & Improvements       8,571,000    
Costs capitalized subsequent to acquisition       915,000    
Gross amount at which carried at close of period [Abstract]            
Land       684,000    
Buildings & Improvements       9,429,000    
Total 10,113,000     10,113,000    
Accumulated Depreciation $ (2,767,000)     (2,767,000)    
Date of Construction or Acquisition 2003          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 10,113,000          
Deductions during year [Abstract]            
Balance at close of year 2,767,000          
Discontinued Operations [Member] | Three Paramount Plaza - Bloomington, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       0    
Initial Cost to Company [Abstract]            
Land       1,261,000    
Buildings & Improvements       6,149,000    
Costs capitalized subsequent to acquisition       1,961,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,482,000    
Buildings & Improvements       7,889,000    
Total 9,371,000     9,371,000    
Accumulated Depreciation $ (3,085,000)     (3,085,000)    
Date of Construction or Acquisition 2002          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 9,371,000          
Deductions during year [Abstract]            
Balance at close of year 3,085,000          
Discontinued Operations [Member] | Timberlands - Leawood, KS [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       1,315,000    
Initial Cost to Company [Abstract]            
Land       2,375,000    
Buildings & Improvements       9,601,000    
Costs capitalized subsequent to acquisition       189,000    
Gross amount at which carried at close of period [Abstract]            
Land       2,375,000    
Buildings & Improvements       9,790,000    
Total 12,165,000     12,165,000    
Accumulated Depreciation $ (242,000)     (242,000)    
Date of Construction or Acquisition 2006          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 12,165,000          
Deductions during year [Abstract]            
Balance at close of year 242,000          
Discontinued Operations [Member] | UHC Office - International Falls, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       800,000    
Initial Cost to Company [Abstract]            
Land       119,000    
Buildings & Improvements       2,366,000    
Costs capitalized subsequent to acquisition       230,000    
Gross amount at which carried at close of period [Abstract]            
Land       119,000    
Buildings & Improvements       2,596,000    
Total 2,715,000     2,715,000    
Accumulated Depreciation $ (734,000)     (734,000)    
Date of Construction or Acquisition 2004          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 2,715,000          
Deductions during year [Abstract]            
Balance at close of year 734,000          
Discontinued Operations [Member] | US Bank Financial Center - Bloomington, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       12,766,000    
Initial Cost to Company [Abstract]            
Land       3,117,000    
Buildings & Improvements       13,350,000    
Costs capitalized subsequent to acquisition       2,023,000    
Gross amount at which carried at close of period [Abstract]            
Land       3,195,000    
Buildings & Improvements       15,295,000    
Total 18,490,000     18,490,000    
Accumulated Depreciation $ (3,805,000)     (3,805,000)    
Date of Construction or Acquisition 2005          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 18,490,000          
Deductions during year [Abstract]            
Balance at close of year 3,805,000          
Discontinued Operations [Member] | Wells Fargo Center - St Cloud, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       5,787,000    
Initial Cost to Company [Abstract]            
Land       869,000    
Buildings & Improvements       8,373,000    
Costs capitalized subsequent to acquisition       1,956,000    
Gross amount at which carried at close of period [Abstract]            
Land       884,000    
Buildings & Improvements       10,314,000    
Total 11,198,000     11,198,000    
Accumulated Depreciation $ (2,641,000)     (2,641,000)    
Date of Construction or Acquisition 2005          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 11,198,000          
Deductions during year [Abstract]            
Balance at close of year 2,641,000          
Discontinued Operations [Member] | West River Business Park - Waite Park, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       0    
Initial Cost to Company [Abstract]            
Land       235,000    
Buildings & Improvements       1,195,000    
Costs capitalized subsequent to acquisition       267,000    
Gross amount at which carried at close of period [Abstract]            
Land       235,000    
Buildings & Improvements       1,462,000    
Total 1,697,000     1,697,000    
Accumulated Depreciation $ (430,000)     (430,000)    
Date of Construction or Acquisition 2003          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,697,000          
Deductions during year [Abstract]            
Balance at close of year 430,000          
Discontinued Operations [Member] | Westgate - Boise, ID [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       3,844,000    
Initial Cost to Company [Abstract]            
Land       1,000,000    
Buildings & Improvements       10,618,000    
Costs capitalized subsequent to acquisition       1,933,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,000,000    
Buildings & Improvements       12,551,000    
Total 13,551,000     13,551,000    
Accumulated Depreciation $ (4,512,000)     (4,512,000)    
Date of Construction or Acquisition 2003          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 13,551,000          
Deductions during year [Abstract]            
Balance at close of year 4,512,000          
Discontinued Operations [Member] | Woodlands Plaza IV - Maryland Heights, MO [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       4,360,000    
Initial Cost to Company [Abstract]            
Land       771,000    
Buildings & Improvements       4,609,000    
Costs capitalized subsequent to acquisition       1,461,000    
Gross amount at which carried at close of period [Abstract]            
Land       862,000    
Buildings & Improvements       5,979,000    
Total 6,841,000     6,841,000    
Accumulated Depreciation $ (1,501,000)     (1,501,000)    
Date of Construction or Acquisition 2006          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 6,841,000          
Deductions during year [Abstract]            
Balance at close of year 1,501,000          
Discontinued Operations [Member] | Barry Pointe Office Park - Kansas City, MO [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       1,369,000    
Initial Cost to Company [Abstract]            
Land       384,000    
Buildings & Improvements       2,366,000    
Costs capitalized subsequent to acquisition       226,000    
Gross amount at which carried at close of period [Abstract]            
Land       392,000    
Buildings & Improvements       2,584,000    
Total 2,976,000     2,976,000    
Accumulated Depreciation $ (547,000)     (547,000)    
Date of Construction or Acquisition 2007          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 2,976,000          
Deductions during year [Abstract]            
Balance at close of year 547,000          
Discontinued Operations [Member] | Burnsville 1 Strip Center - Burnsville, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       0    
Initial Cost to Company [Abstract]            
Land       208,000    
Buildings & Improvements       773,000    
Costs capitalized subsequent to acquisition       200,000    
Gross amount at which carried at close of period [Abstract]            
Land       208,000    
Buildings & Improvements       973,000    
Total 1,181,000     1,181,000    
Accumulated Depreciation $ (306,000)     (306,000)    
Date of Construction or Acquisition 2003          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,181,000          
Deductions during year [Abstract]            
Balance at close of year 306,000          
Discontinued Operations [Member] | Champlin South Pond - Champlin, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       1,185,000    
Initial Cost to Company [Abstract]            
Land       842,000    
Buildings & Improvements       2,703,000    
Costs capitalized subsequent to acquisition       105,000    
Gross amount at which carried at close of period [Abstract]            
Land       866,000    
Buildings & Improvements       2,784,000    
Total 3,650,000     3,650,000    
Accumulated Depreciation $ (797,000)     (797,000)    
Date of Construction or Acquisition 2004          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 3,650,000          
Deductions during year [Abstract]            
Balance at close of year 797,000          
Discontinued Operations [Member] | Chan West Village - Chanhassen, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       12,307,000    
Initial Cost to Company [Abstract]            
Land       5,035,000    
Buildings & Improvements       14,665,000    
Costs capitalized subsequent to acquisition       2,079,000    
Gross amount at which carried at close of period [Abstract]            
Land       5,679,000    
Buildings & Improvements       16,100,000    
Total 21,779,000     21,779,000    
Accumulated Depreciation $ (5,215,000)     (5,215,000)    
Date of Construction or Acquisition 2003          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 21,779,000          
Deductions during year [Abstract]            
Balance at close of year 5,215,000          
Discontinued Operations [Member] | Duluth 4615 Grand - Duluth, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       544,000    
Initial Cost to Company [Abstract]            
Land       130,000    
Buildings & Improvements       1,800,000    
Costs capitalized subsequent to acquisition       156,000    
Gross amount at which carried at close of period [Abstract]            
Land       131,000    
Buildings & Improvements       1,955,000    
Total 2,086,000     2,086,000    
Accumulated Depreciation $ (499,000)     (499,000)    
Date of Construction or Acquisition 2004          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 2,086,000          
Deductions during year [Abstract]            
Balance at close of year 499,000          
Discontinued Operations [Member] | Duluth Denfeld Retail - Duluth, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       1,798,000    
Initial Cost to Company [Abstract]            
Land       276,000    
Buildings & Improvements       4,699,000    
Costs capitalized subsequent to acquisition       185,000    
Gross amount at which carried at close of period [Abstract]            
Land       297,000    
Buildings & Improvements       4,863,000    
Total 5,160,000     5,160,000    
Accumulated Depreciation $ (1,380,000)     (1,380,000)    
Date of Construction or Acquisition 2004          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 5,160,000          
Deductions during year [Abstract]            
Balance at close of year 1,380,000          
Discontinued Operations [Member] | Forest Lake Auto - Forest Lake, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       0    
Initial Cost to Company [Abstract]            
Land       50,000    
Buildings & Improvements       446,000    
Costs capitalized subsequent to acquisition       13,000    
Gross amount at which carried at close of period [Abstract]            
Land       50,000    
Buildings & Improvements       459,000    
Total 509,000     509,000    
Accumulated Depreciation $ (143,000)     (143,000)    
Date of Construction or Acquisition 2003          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 509,000          
Deductions during year [Abstract]            
Balance at close of year 143,000          
Discontinued Operations [Member] | Forest Lake Westlake Center - Forest Lake, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       0    
Initial Cost to Company [Abstract]            
Land       2,446,000    
Buildings & Improvements       5,304,000    
Costs capitalized subsequent to acquisition       1,747,000    
Gross amount at which carried at close of period [Abstract]            
Land       2,480,000    
Buildings & Improvements       7,017,000    
Total 9,497,000     9,497,000    
Accumulated Depreciation $ (1,830,000)     (1,830,000)    
Date of Construction or Acquisition 2003          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 9,497,000          
Deductions during year [Abstract]            
Balance at close of year 1,830,000          
Discontinued Operations [Member] | Grand Forks Medpark Mall - Grand Forks, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       0    
Initial Cost to Company [Abstract]            
Land       681,000    
Buildings & Improvements       4,808,000    
Costs capitalized subsequent to acquisition       231,000    
Gross amount at which carried at close of period [Abstract]            
Land       722,000    
Buildings & Improvements       4,998,000    
Total 5,720,000     5,720,000    
Accumulated Depreciation $ (1,924,000)     (1,924,000)    
Date of Construction or Acquisition 2000          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 5,720,000          
Deductions during year [Abstract]            
Balance at close of year 1,924,000          
Discontinued Operations [Member] | Jamestown Buffalo Mall - Jamestown, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       1,717,000    
Initial Cost to Company [Abstract]            
Land       566,000    
Buildings & Improvements       5,551,000    
Costs capitalized subsequent to acquisition       2,975,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,114,000    
Buildings & Improvements       7,978,000    
Total 9,092,000     9,092,000    
Accumulated Depreciation $ (1,996,000)     (1,996,000)    
Date of Construction or Acquisition 2003          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 9,092,000          
Deductions during year [Abstract]            
Balance at close of year 1,996,000          
Discontinued Operations [Member] | Jamestown Business Center - Jamestown, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       327,000    
Initial Cost to Company [Abstract]            
Land       297,000    
Buildings & Improvements       1,023,000    
Costs capitalized subsequent to acquisition       1,312,000    
Gross amount at which carried at close of period [Abstract]            
Land       333,000    
Buildings & Improvements       2,299,000    
Total 2,632,000     2,632,000    
Accumulated Depreciation $ (965,000)     (965,000)    
Date of Construction or Acquisition 2003          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 2,632,000          
Deductions during year [Abstract]            
Balance at close of year 965,000          
Discontinued Operations [Member] | Lakeville Strip Center - Lakeville, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       0    
Initial Cost to Company [Abstract]            
Land       46,000    
Buildings & Improvements       1,142,000    
Costs capitalized subsequent to acquisition       955,000    
Gross amount at which carried at close of period [Abstract]            
Land       94,000    
Buildings & Improvements       2,049,000    
Total 2,143,000     2,143,000    
Accumulated Depreciation $ (726,000)     (726,000)    
Date of Construction or Acquisition 2003          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 2,143,000          
Deductions during year [Abstract]            
Balance at close of year 726,000          
Discontinued Operations [Member] | Monticello C Store - Monticello, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       0    
Initial Cost to Company [Abstract]            
Land       65,000    
Buildings & Improvements       770,000    
Costs capitalized subsequent to acquisition       37,000    
Gross amount at which carried at close of period [Abstract]            
Land       97,000    
Buildings & Improvements       775,000    
Total 872,000     872,000    
Accumulated Depreciation $ (247,000)     (247,000)    
Date of Construction or Acquisition 2003          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 872,000          
Deductions during year [Abstract]            
Balance at close of year 247,000          
Discontinued Operations [Member] | Omaha Barnes & Noble - Omaha, NE [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       0    
Initial Cost to Company [Abstract]            
Land       600,000    
Buildings & Improvements       3,099,000    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       600,000    
Buildings & Improvements       3,099,000    
Total 3,699,000     3,699,000    
Accumulated Depreciation $ (1,511,000)     (1,511,000)    
Date of Construction or Acquisition 1995          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 3,699,000          
Deductions during year [Abstract]            
Balance at close of year 1,511,000          
Discontinued Operations [Member] | Pine City C-Store - Pine City, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       0    
Initial Cost to Company [Abstract]            
Land       83,000    
Buildings & Improvements       357,000    
Costs capitalized subsequent to acquisition       12,000    
Gross amount at which carried at close of period [Abstract]            
Land       83,000    
Buildings & Improvements       369,000    
Total 452,000     452,000    
Accumulated Depreciation $ (118,000)     (118,000)    
Date of Construction or Acquisition 2003          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 452,000          
Deductions during year [Abstract]            
Balance at close of year 118,000          
Discontinued Operations [Member] | Pine City Evergreen Square - Pine City, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       0    
Initial Cost to Company [Abstract]            
Land       154,000    
Buildings & Improvements       2,646,000    
Costs capitalized subsequent to acquisition       1,334,000    
Gross amount at which carried at close of period [Abstract]            
Land       385,000    
Buildings & Improvements       3,749,000    
Total 4,134,000     4,134,000    
Accumulated Depreciation $ (1,104,000)     (1,104,000)    
Date of Construction or Acquisition 2003          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 4,134,000          
Deductions during year [Abstract]            
Balance at close of year 1,104,000          
Discontinued Operations [Member] | Rochester Maplewood Square - Rochester, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       6,325,000    
Initial Cost to Company [Abstract]            
Land       3,275,000    
Buildings & Improvements       8,610,000    
Costs capitalized subsequent to acquisition       2,155,000    
Gross amount at which carried at close of period [Abstract]            
Land       3,652,000    
Buildings & Improvements       10,388,000    
Total 14,040,000     14,040,000    
Accumulated Depreciation $ (3,936,000)     (3,936,000)    
Date of Construction or Acquisition 1999          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 14,040,000          
Deductions during year [Abstract]            
Balance at close of year 3,936,000          
Discontinued Operations [Member] | St. Cloud Westgate - St. Cloud, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       0    
Initial Cost to Company [Abstract]            
Land       885,000    
Buildings & Improvements       5,535,000    
Costs capitalized subsequent to acquisition       1,396,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,002,000    
Buildings & Improvements       6,814,000    
Total 7,816,000     7,816,000    
Accumulated Depreciation $ (1,827,000)     (1,827,000)    
Date of Construction or Acquisition 2004          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 7,816,000          
Deductions during year [Abstract]            
Balance at close of year 1,827,000          
Wholly Owned Properties [Member]            
Gross amount at which carried at close of period [Abstract]            
Total 1,450,216,000 $ 1,450,216,000 $ 1,303,393,000 1,546,367,000 1,450,216,000 1,435,574,000
Accumulated Depreciation (302,405,000) (302,405,000) (258,809,000) (313,308,000) (302,405,000) (289,624,000)
Reconciliations of total real estate carrying value [Abstract]            
Balance at beginning of year 1,450,216,000 1,435,574,000 1,303,393,000      
Improvements and Other 22,665,000 24,619,000 27,037,000      
Total Additions 1,668,218,000 1,562,315,000 1,462,551,000      
Cost of real estate sold (15,719,000) (85,030,000) (21,953,000)      
Impairment charge (1,566,000) (8,322,000) (305,000)      
Write down of asset and accumulated depreciation on impaired assets (881,000) (6,291,000) 0      
Transfers (97,824,000) (10,307,000) (1,893,000)      
Other [3] (5,861,000) (2,149,000) (2,826,000)      
Balance at close of year 1,546,367,000 1,450,216,000 1,435,574,000      
Reconciliations of accumulated depreciation/amortization [Abstract]            
Balance at beginning of year 302,405,000 289,624,000 258,809,000      
Additions during year [Abstract]            
Provisions for depreciation 45,498,000 40,450,000 40,032,000      
Deductions during year [Abstract]            
Accumulated depreciation on real estate sold (29,463,000) (19,413,000) (6,444,000)      
Write down of asset and accumulated depreciation on impaired assets (881,000) (6,291,000) 0      
Other [3] (4,251,000) (1,965,000) (2,773,000)      
Balance at close of year 313,308,000 302,405,000 289,624,000      
Development in Progress [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       11,789,000    
Buildings & Improvements       125,872,000    
Costs capitalized subsequent to acquisition       16,333,000    
Gross amount at which carried at close of period [Abstract]            
Land       11,789,000    
Buildings & Improvements       142,205,000    
Total 153,994,000 104,609,000 27,599,000 153,994,000 104,609,000 46,782,000
Accumulated Depreciation 0     0    
Reconciliations of total real estate carrying value [Abstract]            
Balance at beginning of year 104,609,000 46,782,000 27,599,000      
Acquisitions 12,647,000 2,079,000 9,177,000      
Improvements and Other 189,306,000 123,240,000 52,970,000      
Involuntary conversion 0 (7,052,000) 0      
Transfers 7,015,000 2,870,000 0      
Development placed in service [4] (159,578,000) (63,210,000) (42,964,000)      
Other [5] (5,000) (100,000) 0      
Balance at close of year 153,994,000 104,609,000 46,782,000      
Deductions during year [Abstract]            
Balance at close of year 0          
Development in Progress [Member] | 71 France - Edina, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       4,721,000    
Buildings & Improvements       27,655,000    
Costs capitalized subsequent to acquisition       2,761,000    
Gross amount at which carried at close of period [Abstract]            
Land       4,721,000    
Buildings & Improvements       30,416,000    
Total 35,137,000     35,137,000    
Accumulated Depreciation $ 0     0    
Date of Construction or Acquisition 2014          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 35,137,000          
Deductions during year [Abstract]            
Balance at close of year 0          
Development in Progress [Member] | Cardinal Point - Grand Forks, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       1,600,000    
Buildings & Improvements       21,455,000    
Costs capitalized subsequent to acquisition       3,395,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,600,000    
Buildings & Improvements       24,850,000    
Total 26,450,000     26,450,000    
Accumulated Depreciation $ 0     0    
Date of Construction or Acquisition 2013          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 26,450,000          
Deductions during year [Abstract]            
Balance at close of year 0          
Development in Progress [Member] | Chateau II - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       240,000    
Buildings & Improvements       12,080,000    
Costs capitalized subsequent to acquisition       809,000    
Gross amount at which carried at close of period [Abstract]            
Land       240,000    
Buildings & Improvements       12,889,000    
Total 13,129,000     13,129,000    
Accumulated Depreciation $ 0     0    
Date of Construction or Acquisition 2013          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 13,129,000          
Deductions during year [Abstract]            
Balance at close of year 0          
Development in Progress [Member] | Deer Ridge - Jamestown, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       711,000    
Buildings & Improvements       13,580,000    
Costs capitalized subsequent to acquisition       1,064,000    
Gross amount at which carried at close of period [Abstract]            
Land       711,000    
Buildings & Improvements       14,644,000    
Total 15,355,000     15,355,000    
Accumulated Depreciation $ 0     0    
Date of Construction or Acquisition 2013          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 15,355,000          
Deductions during year [Abstract]            
Balance at close of year 0          
Development in Progress [Member] | Edina 6565 France SMC III - Edina, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       0    
Buildings & Improvements       20,799,000    
Costs capitalized subsequent to acquisition       1,750,000    
Gross amount at which carried at close of period [Abstract]            
Land       0    
Buildings & Improvements       22,549,000    
Total 22,549,000     22,549,000    
Accumulated Depreciation $ 0     0    
Date of Construction or Acquisition 2014          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 22,549,000          
Deductions during year [Abstract]            
Balance at close of year 0          
Development in Progress [Member] | Minot Southgate Retail - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       889,000    
Buildings & Improvements       1,199,000    
Costs capitalized subsequent to acquisition       76,000    
Gross amount at which carried at close of period [Abstract]            
Land       889,000    
Buildings & Improvements       1,275,000    
Total 2,164,000     2,164,000    
Accumulated Depreciation $ 0     0    
Date of Construction or Acquisition 2014          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 2,164,000          
Deductions during year [Abstract]            
Balance at close of year 0          
Development in Progress [Member] | Other [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       402,000    
Buildings & Improvements       3,233,000    
Costs capitalized subsequent to acquisition       2,983,000    
Gross amount at which carried at close of period [Abstract]            
Land       402,000    
Buildings & Improvements       6,216,000    
Total 6,618,000     6,618,000    
Accumulated Depreciation 0     0    
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year 6,618,000          
Deductions during year [Abstract]            
Balance at close of year 0          
Development in Progress [Member] | PrairieCare Medical - Brooklyn Park, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       2,610,000    
Buildings & Improvements       14,715,000    
Costs capitalized subsequent to acquisition       2,132,000    
Gross amount at which carried at close of period [Abstract]            
Land       2,610,000    
Buildings & Improvements       16,847,000    
Total 19,457,000     19,457,000    
Accumulated Depreciation $ 0     0    
Date of Construction or Acquisition 2014          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 19,457,000          
Deductions during year [Abstract]            
Balance at close of year 0          
Development in Progress [Member] | Renaissance Heights - Williston ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       616,000    
Buildings & Improvements       11,156,000    
Costs capitalized subsequent to acquisition       1,363,000    
Gross amount at which carried at close of period [Abstract]            
Land       616,000    
Buildings & Improvements       12,519,000    
Total 13,135,000     13,135,000    
Accumulated Depreciation $ 0     0    
Date of Construction or Acquisition 2013          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 13,135,000          
Deductions during year [Abstract]            
Balance at close of year 0          
Unimproved Land [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       23,564,000    
Buildings & Improvements       0    
Costs capitalized subsequent to acquisition       2,263,000    
Gross amount at which carried at close of period [Abstract]            
Land       25,827,000    
Buildings & Improvements       0    
Total 25,827,000 21,503,000 21,503,000 25,827,000 $ 22,864,000 $ 21,503,000
Accumulated Depreciation 0     0    
Reconciliations of total real estate carrying value [Abstract]            
Balance at beginning of year 22,864,000 21,503,000 10,990,000      
Acquisitions 10,487,000 3,022,000 13,329,000      
Improvements and Other 1,533,000 1,209,000 854,000      
Cost of real estate sold (670,000) 0 0      
Impairment charge (1,293,000) 0 0      
Transfers (79,000) 0 0      
Balance at close of year 25,827,000 22,864,000 21,503,000      
Deductions during year [Abstract]            
Balance at close of year 0          
Unimproved Land [Member] | Legends at Heritage Place - Sartell, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       537,000    
Buildings & Improvements       0    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       537,000    
Buildings & Improvements       0    
Total 537,000     537,000    
Accumulated Depreciation $ 0     0    
Date of Construction or Acquisition 2013          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 537,000          
Deductions during year [Abstract]            
Balance at close of year 0          
Unimproved Land [Member] | Spring Creek Fruitland - Fruitland, ID [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       339,000    
Buildings & Improvements       0    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       339,000    
Buildings & Improvements       0    
Total 339,000     339,000    
Accumulated Depreciation $ 0     0    
Date of Construction or Acquisition 2014          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 339,000          
Deductions during year [Abstract]            
Balance at close of year 0          
Unimproved Land [Member] | Badger Hills - Rochester, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       1,050,000    
Buildings & Improvements       0    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       1,050,000    
Buildings & Improvements       0    
Total 1,050,000     1,050,000    
Accumulated Depreciation $ 0     0    
Date of Construction or Acquisition 2012          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,050,000          
Deductions during year [Abstract]            
Balance at close of year 0          
Unimproved Land [Member] | Bismarck 4916 - Bismarck, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       3,250,000    
Buildings & Improvements       0    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       3,250,000    
Buildings & Improvements       0    
Total 3,250,000     3,250,000    
Accumulated Depreciation $ 0     0    
Date of Construction or Acquisition 2013          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 3,250,000          
Deductions during year [Abstract]            
Balance at close of year 0          
Unimproved Land [Member] | Bismarck 700 E Main - Bismarck, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       314,000    
Buildings & Improvements       0    
Costs capitalized subsequent to acquisition       565,000    
Gross amount at which carried at close of period [Abstract]            
Land       879,000    
Buildings & Improvements       0    
Total 879,000     879,000    
Accumulated Depreciation $ 0     0    
Date of Construction or Acquisition 2008          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 879,000          
Deductions during year [Abstract]            
Balance at close of year 0          
Unimproved Land [Member] | Creekside Crossing - Bismarck, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       4,286,000    
Buildings & Improvements       0    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       4,286,000    
Buildings & Improvements       0    
Total 4,286,000     4,286,000    
Accumulated Depreciation $ 0     0    
Date of Construction or Acquisition 2014          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 4,286,000          
Deductions during year [Abstract]            
Balance at close of year 0          
Unimproved Land [Member] | Georgetown Square - Grand Chute, WI [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       1,860,000    
Buildings & Improvements       0    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       1,860,000    
Buildings & Improvements       0    
Total 1,860,000     1,860,000    
Accumulated Depreciation $ 0     0    
Date of Construction or Acquisition 2006          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,860,000          
Deductions during year [Abstract]            
Balance at close of year 0          
Unimproved Land [Member] | Grand Forks Grand Forks, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       4,278,000    
Buildings & Improvements       0    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       4,278,000    
Buildings & Improvements       0    
Total 4,278,000     4,278,000    
Accumulated Depreciation $ 0     0    
Date of Construction or Acquisition 2012          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 4,278,000          
Deductions during year [Abstract]            
Balance at close of year 0          
Unimproved Land [Member] | Isanti Unimproved - Isanti, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       58,000    
Buildings & Improvements       0    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       58,000    
Buildings & Improvements       0    
Total 58,000     58,000    
Accumulated Depreciation $ 0     0    
Date of Construction or Acquisition 2014          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 58,000          
Deductions during year [Abstract]            
Balance at close of year 0          
Unimproved Land [Member] | Minot 1525 24th Ave SW - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       1,262,000    
Buildings & Improvements       0    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       1,262,000    
Buildings & Improvements       0    
Total 1,262,000     1,262,000    
Accumulated Depreciation $ 0     0    
Date of Construction or Acquisition 2014          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,262,000          
Deductions during year [Abstract]            
Balance at close of year 0          
Unimproved Land [Member] | Monticello - Monticello, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       115,000    
Buildings & Improvements       0    
Costs capitalized subsequent to acquisition       3,000    
Gross amount at which carried at close of period [Abstract]            
Land       118,000    
Buildings & Improvements       0    
Total 118,000     118,000    
Accumulated Depreciation $ 0     0    
Date of Construction or Acquisition 2006          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 118,000          
Deductions during year [Abstract]            
Balance at close of year 0          
Unimproved Land [Member] | Monticello 7th Addition - Monticello, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       1,734,000    
Buildings & Improvements       0    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       1,734,000    
Buildings & Improvements       0    
Total 1,734,000     1,734,000    
Accumulated Depreciation $ 0     0    
Date of Construction or Acquisition 2014          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,734,000          
Deductions during year [Abstract]            
Balance at close of year 0          
Unimproved Land [Member] | Rapid City Unimproved- Rapid City, SD [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       1,376,000    
Buildings & Improvements       0    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       1,376,000    
Buildings & Improvements       0    
Total 1,376,000     1,376,000    
Accumulated Depreciation $ 0     0    
Date of Construction or Acquisition 2014          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,376,000          
Deductions during year [Abstract]            
Balance at close of year 0          
Unimproved Land [Member] | Renaissance Heights - Williston ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       2,229,000    
Buildings & Improvements       0    
Costs capitalized subsequent to acquisition       1,581,000    
Gross amount at which carried at close of period [Abstract]            
Land       3,810,000    
Buildings & Improvements       0    
Total 3,810,000     3,810,000    
Accumulated Depreciation $ 0     0    
Date of Construction or Acquisition 2012          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 3,810,000          
Deductions during year [Abstract]            
Balance at close of year 0          
Unimproved Land [Member] | River Falls - River Falls, WI [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       176,000    
Buildings & Improvements       0    
Costs capitalized subsequent to acquisition       5,000    
Gross amount at which carried at close of period [Abstract]            
Land       181,000    
Buildings & Improvements       0    
Total 181,000     181,000    
Accumulated Depreciation $ 0     0    
Date of Construction or Acquisition 2003          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 181,000          
Deductions during year [Abstract]            
Balance at close of year 0          
Unimproved Land [Member] | TCA - Eagan, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       325,000    
Buildings & Improvements       0    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       325,000    
Buildings & Improvements       0    
Total 325,000     325,000    
Accumulated Depreciation $ 0     0    
Date of Construction or Acquisition 2006          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 325,000          
Deductions during year [Abstract]            
Balance at close of year 0          
Unimproved Land [Member] | Urbandale - Urbandale, IA [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       5,000    
Buildings & Improvements       0    
Costs capitalized subsequent to acquisition       109,000    
Gross amount at which carried at close of period [Abstract]            
Land       114,000    
Buildings & Improvements       0    
Total 114,000     114,000    
Accumulated Depreciation $ 0     0    
Date of Construction or Acquisition 2009          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 114,000          
Deductions during year [Abstract]            
Balance at close of year 0          
Unimproved Land [Member] | Weston - Weston, WI [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       370,000    
Buildings & Improvements       0    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       370,000    
Buildings & Improvements       0    
Total 370,000     370,000    
Accumulated Depreciation $ 0     0    
Date of Construction or Acquisition 2006          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 370,000          
Deductions during year [Abstract]            
Balance at close of year 0          
Unimproved Land Moved to Development in Progress [Member]            
Reconciliations of total real estate carrying value [Abstract]            
Transfers (7,015,000) (2,870,000) (3,670,000)      
Multi-Family Residential [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       423,385,000    
Initial Cost to Company [Abstract]            
Land       65,410,000    
Buildings & Improvements       746,299,000    
Costs capitalized subsequent to acquisition       134,811,000    
Gross amount at which carried at close of period [Abstract]            
Land       81,919,000    
Buildings & Improvements       864,601,000    
Total 946,520,000     946,520,000    
Accumulated Depreciation (180,414,000)     (180,414,000)    
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year 946,520,000          
Deductions during year [Abstract]            
Balance at close of year 180,414,000          
Multi-Family Residential [Member] | 11th Street 3 Plex - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       84,000    
Initial Cost to Company [Abstract]            
Land       11,000    
Buildings & Improvements       53,000    
Costs capitalized subsequent to acquisition       19,000    
Gross amount at which carried at close of period [Abstract]            
Land       20,000    
Buildings & Improvements       63,000    
Total 83,000     83,000    
Accumulated Depreciation $ (12,000)     (12,000)    
Date of Construction or Acquisition 2008          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 83,000          
Deductions during year [Abstract]            
Balance at close of year 12,000          
Multi-Family Residential [Member] | 4th Street 4 Plex - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       98,000    
Initial Cost to Company [Abstract]            
Land       15,000    
Buildings & Improvements       74,000    
Costs capitalized subsequent to acquisition       34,000    
Gross amount at which carried at close of period [Abstract]            
Land       23,000    
Buildings & Improvements       100,000    
Total 123,000     123,000    
Accumulated Depreciation $ (19,000)     (19,000)    
Date of Construction or Acquisition 2008          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 123,000          
Deductions during year [Abstract]            
Balance at close of year 19,000          
Multi-Family Residential [Member] | Alps Park - Rapid City, SD [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       3,934,000    
Initial Cost to Company [Abstract]            
Land       287,000    
Buildings & Improvements       5,551,000    
Costs capitalized subsequent to acquisition       165,000    
Gross amount at which carried at close of period [Abstract]            
Land       293,000    
Buildings & Improvements       5,710,000    
Total 6,003,000     6,003,000    
Accumulated Depreciation $ (299,000)     (299,000)    
Date of Construction or Acquisition 2013          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 6,003,000          
Deductions during year [Abstract]            
Balance at close of year 299,000          
Multi-Family Residential [Member] | Apartments on Main - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       642,000    
Initial Cost to Company [Abstract]            
Land       158,000    
Buildings & Improvements       1,123,000    
Costs capitalized subsequent to acquisition       53,000    
Gross amount at which carried at close of period [Abstract]            
Land       193,000    
Buildings & Improvements       1,141,000    
Total 1,334,000     1,334,000    
Accumulated Depreciation $ (235,000)     (235,000)    
Date of Construction or Acquisition 1987          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,334,000          
Deductions during year [Abstract]            
Balance at close of year $ 235,000          
Multi-Family Residential [Member] | Apartments on Main - Minot, ND [Member] | Minimum [Member]            
Gross amount at which carried at close of period [Abstract]            
Life on which depreciation in latest income statement is computed 24 years          
Multi-Family Residential [Member] | Apartments on Main - Minot, ND [Member] | Maximum [Member]            
Gross amount at which carried at close of period [Abstract]            
Life on which depreciation in latest income statement is computed 40 years          
Multi-Family Residential [Member] | Arbors - S Sioux City, NE [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       3,840,000    
Initial Cost to Company [Abstract]            
Land       350,000    
Buildings & Improvements       6,625,000    
Costs capitalized subsequent to acquisition       1,923,000    
Gross amount at which carried at close of period [Abstract]            
Land       980,000    
Buildings & Improvements       7,918,000    
Total $ 8,898,000     8,898,000    
Accumulated Depreciation $ (2,115,000)     (2,115,000)    
Date of Construction or Acquisition 2006          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 8,898,000          
Deductions during year [Abstract]            
Balance at close of year 2,115,000          
Multi-Family Residential [Member] | Arcata - Golden Valley, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       2,088,000    
Buildings & Improvements       29,640,000    
Costs capitalized subsequent to acquisition       95,000    
Gross amount at which carried at close of period [Abstract]            
Land       2,088,000    
Buildings & Improvements       29,735,000    
Total 31,823,000     31,823,000    
Accumulated Depreciation $ (380,000)     (380,000)    
Date of Construction or Acquisition 2013          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 31,823,000          
Deductions during year [Abstract]            
Balance at close of year 380,000          
Multi-Family Residential [Member] | Ashland - Grand Forks, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       5,517,000    
Initial Cost to Company [Abstract]            
Land       741,000    
Buildings & Improvements       7,569,000    
Costs capitalized subsequent to acquisition       163,000    
Gross amount at which carried at close of period [Abstract]            
Land       774,000    
Buildings & Improvements       7,699,000    
Total 8,473,000     8,473,000    
Accumulated Depreciation $ (678,000)     (678,000)    
Date of Construction or Acquisition 2012          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 8,473,000          
Deductions during year [Abstract]            
Balance at close of year 678,000          
Multi-Family Residential [Member] | Boulder Court - Eagan, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       2,736,000    
Initial Cost to Company [Abstract]            
Land       1,067,000    
Buildings & Improvements       5,498,000    
Costs capitalized subsequent to acquisition       3,005,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,324,000    
Buildings & Improvements       8,246,000    
Total 9,570,000     9,570,000    
Accumulated Depreciation $ (2,539,000)     (2,539,000)    
Date of Construction or Acquisition 2003          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 9,570,000          
Deductions during year [Abstract]            
Balance at close of year 2,539,000          
Multi-Family Residential [Member] | Brookfield Village - Topeka, KS [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       5,216,000    
Initial Cost to Company [Abstract]            
Land       509,000    
Buildings & Improvements       6,698,000    
Costs capitalized subsequent to acquisition       1,539,000    
Gross amount at which carried at close of period [Abstract]            
Land       756,000    
Buildings & Improvements       7,990,000    
Total 8,746,000     8,746,000    
Accumulated Depreciation $ (2,348,000)     (2,348,000)    
Date of Construction or Acquisition 2003          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 8,746,000          
Deductions during year [Abstract]            
Balance at close of year 2,348,000          
Multi-Family Residential [Member] | Brooklyn Heights - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       694,000    
Initial Cost to Company [Abstract]            
Land       145,000    
Buildings & Improvements       1,450,000    
Costs capitalized subsequent to acquisition       879,000    
Gross amount at which carried at close of period [Abstract]            
Land       219,000    
Buildings & Improvements       2,255,000    
Total 2,474,000     2,474,000    
Accumulated Depreciation $ (949,000)     (949,000)    
Date of Construction or Acquisition 1997          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 2,474,000          
Deductions during year [Abstract]            
Balance at close of year $ 949,000          
Multi-Family Residential [Member] | Brooklyn Heights - Minot, ND [Member] | Minimum [Member]            
Gross amount at which carried at close of period [Abstract]            
Life on which depreciation in latest income statement is computed 12 years          
Multi-Family Residential [Member] | Brooklyn Heights - Minot, ND [Member] | Maximum [Member]            
Gross amount at which carried at close of period [Abstract]            
Life on which depreciation in latest income statement is computed 40 years          
Multi-Family Residential [Member] | Campus Center - St. Cloud, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       1,127,000    
Initial Cost to Company [Abstract]            
Land       395,000    
Buildings & Improvements       2,244,000    
Costs capitalized subsequent to acquisition       243,000    
Gross amount at which carried at close of period [Abstract]            
Land       407,000    
Buildings & Improvements       2,475,000    
Total $ 2,882,000     2,882,000    
Accumulated Depreciation $ (534,000)     (534,000)    
Date of Construction or Acquisition 2007          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 2,882,000          
Deductions during year [Abstract]            
Balance at close of year 534,000          
Multi-Family Residential [Member] | Campus Heights - St. Cloud, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       110,000    
Buildings & Improvements       628,000    
Costs capitalized subsequent to acquisition       157,000    
Gross amount at which carried at close of period [Abstract]            
Land       124,000    
Buildings & Improvements       771,000    
Total 895,000     895,000    
Accumulated Depreciation $ (163,000)     (163,000)    
Date of Construction or Acquisition 2007          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 895,000          
Deductions during year [Abstract]            
Balance at close of year 163,000          
Multi-Family Residential [Member] | Campus Knoll - St. Cloud, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       752,000    
Initial Cost to Company [Abstract]            
Land       266,000    
Buildings & Improvements       1,512,000    
Costs capitalized subsequent to acquisition       180,000    
Gross amount at which carried at close of period [Abstract]            
Land       305,000    
Buildings & Improvements       1,653,000    
Total 1,958,000     1,958,000    
Accumulated Depreciation $ (364,000)     (364,000)    
Date of Construction or Acquisition 2007          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,958,000          
Deductions during year [Abstract]            
Balance at close of year 364,000          
Multi-Family Residential [Member] | Campus Plaza - St. Cloud, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       54,000    
Buildings & Improvements       311,000    
Costs capitalized subsequent to acquisition       85,000    
Gross amount at which carried at close of period [Abstract]            
Land       60,000    
Buildings & Improvements       390,000    
Total 450,000     450,000    
Accumulated Depreciation $ (87,000)     (87,000)    
Date of Construction or Acquisition 2007          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 450,000          
Deductions during year [Abstract]            
Balance at close of year 87,000          
Multi-Family Residential [Member] | Campus Side - St. Cloud, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       107,000    
Buildings & Improvements       615,000    
Costs capitalized subsequent to acquisition       161,000    
Gross amount at which carried at close of period [Abstract]            
Land       118,000    
Buildings & Improvements       765,000    
Total 883,000     883,000    
Accumulated Depreciation $ (170,000)     (170,000)    
Date of Construction or Acquisition 2007          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 883,000          
Deductions during year [Abstract]            
Balance at close of year 170,000          
Multi-Family Residential [Member] | Campus View - St. Cloud, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       107,000    
Buildings & Improvements       615,000    
Costs capitalized subsequent to acquisition       156,000    
Gross amount at which carried at close of period [Abstract]            
Land       113,000    
Buildings & Improvements       765,000    
Total 878,000     878,000    
Accumulated Depreciation $ (164,000)     (164,000)    
Date of Construction or Acquisition 2007          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 878,000          
Deductions during year [Abstract]            
Balance at close of year 164,000          
Multi-Family Residential [Member] | Canyon Lake - Rapid City, SD [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       2,843,000    
Initial Cost to Company [Abstract]            
Land       305,000    
Buildings & Improvements       3,958,000    
Costs capitalized subsequent to acquisition       1,652,000    
Gross amount at which carried at close of period [Abstract]            
Land       376,000    
Buildings & Improvements       5,539,000    
Total 5,915,000     5,915,000    
Accumulated Depreciation $ (1,739,000)     (1,739,000)    
Date of Construction or Acquisition 2001          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 5,915,000          
Deductions during year [Abstract]            
Balance at close of year 1,739,000          
Multi-Family Residential [Member] | Castlerock - Billings, MT [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       6,574,000    
Initial Cost to Company [Abstract]            
Land       736,000    
Buildings & Improvements       4,864,000    
Costs capitalized subsequent to acquisition       2,165,000    
Gross amount at which carried at close of period [Abstract]            
Land       994,000    
Buildings & Improvements       6,771,000    
Total 7,765,000     7,765,000    
Accumulated Depreciation $ (2,726,000)     (2,726,000)    
Date of Construction or Acquisition 1998          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 7,765,000          
Deductions during year [Abstract]            
Balance at close of year 2,726,000          
Multi-Family Residential [Member] | Chateau I - Minot ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       61,000    
Buildings & Improvements       5,663,000    
Costs capitalized subsequent to acquisition       683,000    
Gross amount at which carried at close of period [Abstract]            
Land       71,000    
Buildings & Improvements       6,336,000    
Total 6,407,000     6,407,000    
Accumulated Depreciation $ (786,000)     (786,000)    
Date of Construction or Acquisition 2013          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 6,407,000          
Deductions during year [Abstract]            
Balance at close of year 786,000          
Multi-Family Residential [Member] | Cimarron Hills - Omaha, NE [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       4,729,000    
Initial Cost to Company [Abstract]            
Land       706,000    
Buildings & Improvements       9,588,000    
Costs capitalized subsequent to acquisition       4,346,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,334,000    
Buildings & Improvements       13,306,000    
Total 14,640,000     14,640,000    
Accumulated Depreciation $ (4,723,000)     (4,723,000)    
Date of Construction or Acquisition 2001          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 14,640,000          
Deductions during year [Abstract]            
Balance at close of year 4,723,000          
Multi-Family Residential [Member] | Colonial Villa - Burnsville, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       5,473,000    
Initial Cost to Company [Abstract]            
Land       2,401,000    
Buildings & Improvements       11,515,000    
Costs capitalized subsequent to acquisition       7,471,000    
Gross amount at which carried at close of period [Abstract]            
Land       2,844,000    
Buildings & Improvements       18,543,000    
Total 21,387,000     21,387,000    
Accumulated Depreciation $ (5,255,000)     (5,255,000)    
Date of Construction or Acquisition 2003          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 21,387,000          
Deductions during year [Abstract]            
Balance at close of year 5,255,000          
Multi-Family Residential [Member] | Colony - Lincoln, NE [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       13,303,000    
Initial Cost to Company [Abstract]            
Land       1,515,000    
Buildings & Improvements       15,730,000    
Costs capitalized subsequent to acquisition       671,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,574,000    
Buildings & Improvements       16,342,000    
Total 17,916,000     17,916,000    
Accumulated Depreciation $ (1,316,000)     (1,316,000)    
Date of Construction or Acquisition 2012          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 17,916,000          
Deductions during year [Abstract]            
Balance at close of year 1,316,000          
Multi-Family Residential [Member] | Colton Heights - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       391,000    
Initial Cost to Company [Abstract]            
Land       80,000    
Buildings & Improvements       672,000    
Costs capitalized subsequent to acquisition       421,000    
Gross amount at which carried at close of period [Abstract]            
Land       123,000    
Buildings & Improvements       1,050,000    
Total 1,173,000     1,173,000    
Accumulated Depreciation $ (769,000)     (769,000)    
Date of Construction or Acquisition 1984          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,173,000          
Deductions during year [Abstract]            
Balance at close of year 769,000          
Multi-Family Residential [Member] | Commons at Southgate - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       3,691,000    
Buildings & Improvements       31,351,000    
Costs capitalized subsequent to acquisition       580,000    
Gross amount at which carried at close of period [Abstract]            
Land       3,703,000    
Buildings & Improvements       31,919,000    
Total 35,622,000     35,622,000    
Accumulated Depreciation $ (993,000)     (993,000)    
Date of Construction or Acquisition 2013          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 35,622,000          
Deductions during year [Abstract]            
Balance at close of year 993,000          
Multi-Family Residential [Member] | Cornerstone - St. Cloud, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       54,000    
Buildings & Improvements       311,000    
Costs capitalized subsequent to acquisition       88,000    
Gross amount at which carried at close of period [Abstract]            
Land       57,000    
Buildings & Improvements       396,000    
Total 453,000     453,000    
Accumulated Depreciation $ (89,000)     (89,000)    
Date of Construction or Acquisition 2007          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 453,000          
Deductions during year [Abstract]            
Balance at close of year 89,000          
Multi-Family Residential [Member] | Cottage West Twin Homes - Sioux Falls, SD [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       3,586,000    
Initial Cost to Company [Abstract]            
Land       968,000    
Buildings & Improvements       3,762,000    
Costs capitalized subsequent to acquisition       432,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,022,000    
Buildings & Improvements       4,140,000    
Total 5,162,000     5,162,000    
Accumulated Depreciation $ (378,000)     (378,000)    
Date of Construction or Acquisition 2011          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 5,162,000          
Deductions during year [Abstract]            
Balance at close of year 378,000          
Multi-Family Residential [Member] | Cottonwood - Bismarck, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       15,586,000    
Initial Cost to Company [Abstract]            
Land       1,056,000    
Buildings & Improvements       17,372,000    
Costs capitalized subsequent to acquisition       3,294,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,383,000    
Buildings & Improvements       20,339,000    
Total 21,722,000     21,722,000    
Accumulated Depreciation $ (6,904,000)     (6,904,000)    
Date of Construction or Acquisition 1997          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 21,722,000          
Deductions during year [Abstract]            
Balance at close of year 6,904,000          
Multi-Family Residential [Member] | Country Meadows - Billings, MT [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       6,560,000    
Initial Cost to Company [Abstract]            
Land       491,000    
Buildings & Improvements       7,809,000    
Costs capitalized subsequent to acquisition       1,486,000    
Gross amount at which carried at close of period [Abstract]            
Land       538,000    
Buildings & Improvements       9,248,000    
Total 9,786,000     9,786,000    
Accumulated Depreciation $ (3,797,000)     (3,797,000)    
Date of Construction or Acquisition 1995          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 9,786,000          
Deductions during year [Abstract]            
Balance at close of year $ 3,797,000          
Multi-Family Residential [Member] | Country Meadows - Billings, MT [Member] | Minimum [Member]            
Gross amount at which carried at close of period [Abstract]            
Life on which depreciation in latest income statement is computed 33 years          
Multi-Family Residential [Member] | Country Meadows - Billings, MT [Member] | Maximum [Member]            
Gross amount at which carried at close of period [Abstract]            
Life on which depreciation in latest income statement is computed 40 years          
Multi-Family Residential [Member] | Crestview - Bismarck, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       3,839,000    
Initial Cost to Company [Abstract]            
Land       235,000    
Buildings & Improvements       4,290,000    
Costs capitalized subsequent to acquisition       1,682,000    
Gross amount at which carried at close of period [Abstract]            
Land       515,000    
Buildings & Improvements       5,692,000    
Total $ 6,207,000     6,207,000    
Accumulated Depreciation $ (2,915,000)     (2,915,000)    
Date of Construction or Acquisition 1994          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 6,207,000          
Deductions during year [Abstract]            
Balance at close of year $ 2,915,000          
Multi-Family Residential [Member] | Crestview - Bismarck, ND [Member] | Minimum [Member]            
Gross amount at which carried at close of period [Abstract]            
Life on which depreciation in latest income statement is computed 24 years          
Multi-Family Residential [Member] | Crestview - Bismarck, ND [Member] | Maximum [Member]            
Gross amount at which carried at close of period [Abstract]            
Life on which depreciation in latest income statement is computed 40 years          
Multi-Family Residential [Member] | Crown - Rochester, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       2,571,000    
Initial Cost to Company [Abstract]            
Land       261,000    
Buildings & Improvements       3,289,000    
Costs capitalized subsequent to acquisition       246,000    
Gross amount at which carried at close of period [Abstract]            
Land       269,000    
Buildings & Improvements       3,527,000    
Total $ 3,796,000     3,796,000    
Accumulated Depreciation $ (470,000)     (470,000)    
Date of Construction or Acquisition 2010          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 3,796,000          
Deductions during year [Abstract]            
Balance at close of year 470,000          
Multi-Family Residential [Member] | Crown Colony - Topeka, KS [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       8,081,000    
Initial Cost to Company [Abstract]            
Land       620,000    
Buildings & Improvements       9,956,000    
Costs capitalized subsequent to acquisition       2,388,000    
Gross amount at which carried at close of period [Abstract]            
Land       898,000    
Buildings & Improvements       12,066,000    
Total 12,964,000     12,964,000    
Accumulated Depreciation $ (4,531,000)     (4,531,000)    
Date of Construction or Acquisition 1999          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 12,964,000          
Deductions during year [Abstract]            
Balance at close of year 4,531,000          
Multi-Family Residential [Member] | Cypress Court - St. Cloud, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       13,150,000    
Initial Cost to Company [Abstract]            
Land       1,583,000    
Buildings & Improvements       18,874,000    
Costs capitalized subsequent to acquisition       148,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,583,000    
Buildings & Improvements       19,022,000    
Total 20,605,000     20,605,000    
Accumulated Depreciation $ (652,000)     (652,000)    
Date of Construction or Acquisition 2012          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 20,605,000          
Deductions during year [Abstract]            
Balance at close of year 652,000          
Multi-Family Residential [Member] | Dakota Commons - Williston, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1],[6]       0    
Initial Cost to Company [Abstract]            
Land [6]       823,000    
Buildings & Improvements [6]       9,596,000    
Costs capitalized subsequent to acquisition [6]       25,000    
Gross amount at which carried at close of period [Abstract]            
Land [6]       824,000    
Buildings & Improvements [6]       9,620,000    
Total [6] 10,444,000     10,444,000    
Accumulated Depreciation [6] $ (236,000)     (236,000)    
Date of Construction or Acquisition [6] 2012          
Life on which depreciation in latest income statement is computed [6] 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year [6] $ 10,444,000          
Deductions during year [Abstract]            
Balance at close of year [6] 236,000          
Multi-Family Residential [Member] | Evergreen - Isanti, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       1,986,000    
Initial Cost to Company [Abstract]            
Land       380,000    
Buildings & Improvements       2,740,000    
Costs capitalized subsequent to acquisition       116,000    
Gross amount at which carried at close of period [Abstract]            
Land       385,000    
Buildings & Improvements       2,851,000    
Total 3,236,000     3,236,000    
Accumulated Depreciation $ (474,000)     (474,000)    
Date of Construction or Acquisition 2008          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 3,236,000          
Deductions during year [Abstract]            
Balance at close of year 474,000          
Multi-Family Residential [Member] | Evergreen II - Isanti, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       2,066,000    
Initial Cost to Company [Abstract]            
Land       691,000    
Buildings & Improvements       2,784,000    
Costs capitalized subsequent to acquisition       55,000    
Gross amount at which carried at close of period [Abstract]            
Land       698,000    
Buildings & Improvements       2,832,000    
Total 3,530,000     3,530,000    
Accumulated Depreciation $ (277,000)     (277,000)    
Date of Construction or Acquisition 2011          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 3,530,000          
Deductions during year [Abstract]            
Balance at close of year 277,000          
Multi-Family Residential [Member] | Fairmont - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       332,000    
Initial Cost to Company [Abstract]            
Land       28,000    
Buildings & Improvements       337,000    
Costs capitalized subsequent to acquisition       117,000    
Gross amount at which carried at close of period [Abstract]            
Land       55,000    
Buildings & Improvements       427,000    
Total 482,000     482,000    
Accumulated Depreciation $ (76,000)     (76,000)    
Date of Construction or Acquisition 2008          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 482,000          
Deductions during year [Abstract]            
Balance at close of year 76,000          
Multi-Family Residential [Member] | First Avenue - Minot ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       0    
Buildings & Improvements       3,046,000    
Costs capitalized subsequent to acquisition       11,000    
Gross amount at which carried at close of period [Abstract]            
Land       0    
Buildings & Improvements       3,057,000    
Total 3,057,000     3,057,000    
Accumulated Depreciation $ (155,000)     (155,000)    
Date of Construction or Acquisition 2013          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 3,057,000          
Deductions during year [Abstract]            
Balance at close of year 155,000          
Multi-Family Residential [Member] | Forest Park - Grand Forks, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       7,560,000    
Initial Cost to Company [Abstract]            
Land       810,000    
Buildings & Improvements       5,579,000    
Costs capitalized subsequent to acquisition       7,407,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,426,000    
Buildings & Improvements       12,370,000    
Total 13,796,000     13,796,000    
Accumulated Depreciation $ (5,333,000)     (5,333,000)    
Date of Construction or Acquisition 1993          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 13,796,000          
Deductions during year [Abstract]            
Balance at close of year $ 5,333,000          
Multi-Family Residential [Member] | Forest Park - Grand Forks, ND [Member] | Minimum [Member]            
Gross amount at which carried at close of period [Abstract]            
Life on which depreciation in latest income statement is computed 24 years          
Multi-Family Residential [Member] | Forest Park - Grand Forks, ND [Member] | Maximum [Member]            
Gross amount at which carried at close of period [Abstract]            
Life on which depreciation in latest income statement is computed 40 years          
Multi-Family Residential [Member] | Gables Townhomes - Sioux Falls, SD [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       1,452,000    
Initial Cost to Company [Abstract]            
Land       349,000    
Buildings & Improvements       1,921,000    
Costs capitalized subsequent to acquisition       173,000    
Gross amount at which carried at close of period [Abstract]            
Land       374,000    
Buildings & Improvements       2,069,000    
Total $ 2,443,000     2,443,000    
Accumulated Depreciation $ (189,000)     (189,000)    
Date of Construction or Acquisition 2011          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 2,443,000          
Deductions during year [Abstract]            
Balance at close of year 189,000          
Multi-Family Residential [Member] | Grand Gateway - St. Cloud, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       5,345,000    
Initial Cost to Company [Abstract]            
Land       814,000    
Buildings & Improvements       7,086,000    
Costs capitalized subsequent to acquisition       805,000    
Gross amount at which carried at close of period [Abstract]            
Land       934,000    
Buildings & Improvements       7,771,000    
Total 8,705,000     8,705,000    
Accumulated Depreciation $ (746,000)     (746,000)    
Date of Construction or Acquisition 2012          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 8,705,000          
Deductions during year [Abstract]            
Balance at close of year 746,000          
Multi-Family Residential [Member] | Greenfield - Omaha, NE [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       3,552,000    
Initial Cost to Company [Abstract]            
Land       578,000    
Buildings & Improvements       4,122,000    
Costs capitalized subsequent to acquisition       769,000    
Gross amount at which carried at close of period [Abstract]            
Land       803,000    
Buildings & Improvements       4,666,000    
Total 5,469,000     5,469,000    
Accumulated Depreciation $ (932,000)     (932,000)    
Date of Construction or Acquisition 2007          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 5,469,000          
Deductions during year [Abstract]            
Balance at close of year 932,000          
Multi-Family Residential [Member] | Heritage Manor - Rochester, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       3,895,000    
Initial Cost to Company [Abstract]            
Land       403,000    
Buildings & Improvements       6,968,000    
Costs capitalized subsequent to acquisition       2,796,000    
Gross amount at which carried at close of period [Abstract]            
Land       580,000    
Buildings & Improvements       9,587,000    
Total 10,167,000     10,167,000    
Accumulated Depreciation $ (3,751,000)     (3,751,000)    
Date of Construction or Acquisition 1998          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 10,167,000          
Deductions during year [Abstract]            
Balance at close of year 3,751,000          
Multi-Family Residential [Member] | Homestead Garden - Rapid City, SD [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       9,761,000    
Initial Cost to Company [Abstract]            
Land       655,000    
Buildings & Improvements       14,139,000    
Costs capitalized subsequent to acquisition       156,000    
Gross amount at which carried at close of period [Abstract]            
Land       658,000    
Buildings & Improvements       14,292,000    
Total 14,950,000     14,950,000    
Accumulated Depreciation $ (329,000)     (329,000)    
Date of Construction or Acquisition 2014          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 14,950,000          
Deductions during year [Abstract]            
Balance at close of year 329,000          
Multi-Family Residential [Member] | Indian Hills - Sioux City, IA [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       294,000    
Buildings & Improvements       2,921,000    
Costs capitalized subsequent to acquisition       3,709,000    
Gross amount at which carried at close of period [Abstract]            
Land       397,000    
Buildings & Improvements       6,527,000    
Total 6,924,000     6,924,000    
Accumulated Depreciation $ (1,353,000)     (1,353,000)    
Date of Construction or Acquisition 2007          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 6,924,000          
Deductions during year [Abstract]            
Balance at close of year 1,353,000          
Multi-Family Residential [Member] | Kirkwood Manor - Bismarck, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       3,259,000    
Initial Cost to Company [Abstract]            
Land       449,000    
Buildings & Improvements       2,725,000    
Costs capitalized subsequent to acquisition       1,676,000    
Gross amount at which carried at close of period [Abstract]            
Land       553,000    
Buildings & Improvements       4,297,000    
Total 4,850,000     4,850,000    
Accumulated Depreciation $ (1,786,000)     (1,786,000)    
Date of Construction or Acquisition 1997          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 4,850,000          
Deductions during year [Abstract]            
Balance at close of year $ 1,786,000          
Multi-Family Residential [Member] | Kirkwood Manor - Bismarck, ND [Member] | Minimum [Member]            
Gross amount at which carried at close of period [Abstract]            
Life on which depreciation in latest income statement is computed 12 years          
Multi-Family Residential [Member] | Kirkwood Manor - Bismarck, ND [Member] | Maximum [Member]            
Gross amount at which carried at close of period [Abstract]            
Life on which depreciation in latest income statement is computed 40 years          
Multi-Family Residential [Member] | Lakeside Village Lincoln, NE [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       13,129,000    
Initial Cost to Company [Abstract]            
Land       1,215,000    
Buildings & Improvements       15,837,000    
Costs capitalized subsequent to acquisition       442,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,263,000    
Buildings & Improvements       16,231,000    
Total $ 17,494,000     17,494,000    
Accumulated Depreciation $ (1,294,000)     (1,294,000)    
Date of Construction or Acquisition 2012          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 17,494,000          
Deductions during year [Abstract]            
Balance at close of year 1,294,000          
Multi-Family Residential [Member] | Landing at Southgate - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       2,254,000    
Buildings & Improvements       12,955,000    
Costs capitalized subsequent to acquisition       93,000    
Gross amount at which carried at close of period [Abstract]            
Land       2,294,000    
Buildings & Improvements       13,008,000    
Total 15,302,000     15,302,000    
Accumulated Depreciation $ (546,000)     (546,000)    
Date of Construction or Acquisition 2013          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 15,302,000          
Deductions during year [Abstract]            
Balance at close of year 546,000          
Multi-Family Residential [Member] | Landmark - Grand Forks, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       1,573,000    
Initial Cost to Company [Abstract]            
Land       184,000    
Buildings & Improvements       1,514,000    
Costs capitalized subsequent to acquisition       1,093,000    
Gross amount at which carried at close of period [Abstract]            
Land       331,000    
Buildings & Improvements       2,460,000    
Total 2,791,000     2,791,000    
Accumulated Depreciation $ (1,070,000)     (1,070,000)    
Date of Construction or Acquisition 1997          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 2,791,000          
Deductions during year [Abstract]            
Balance at close of year 1,070,000          
Multi-Family Residential [Member] | Legacy - Grand Forks, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       15,528,000    
Initial Cost to Company [Abstract]            
Land       1,362,000    
Buildings & Improvements       21,727,000    
Costs capitalized subsequent to acquisition       6,665,000    
Gross amount at which carried at close of period [Abstract]            
Land       2,133,000    
Buildings & Improvements       27,621,000    
Total 29,754,000     29,754,000    
Accumulated Depreciation (10,186,000)     (10,186,000)    
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year 29,754,000          
Deductions during year [Abstract]            
Balance at close of year $ 10,186,000          
Multi-Family Residential [Member] | Legacy - Grand Forks, ND [Member] | Minimum [Member]            
Gross amount at which carried at close of period [Abstract]            
Date of Construction or Acquisition 1995          
Life on which depreciation in latest income statement is computed 24 years          
Multi-Family Residential [Member] | Legacy - Grand Forks, ND [Member] | Maximum [Member]            
Gross amount at which carried at close of period [Abstract]            
Date of Construction or Acquisition 2005          
Life on which depreciation in latest income statement is computed 40 years          
Multi-Family Residential [Member] | Legacy Heights - Bismarck, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       804,000    
Buildings & Improvements       9,162,000    
Costs capitalized subsequent to acquisition       73,000    
Gross amount at which carried at close of period [Abstract]            
Land       804,000    
Buildings & Improvements       9,235,000    
Total $ 10,039,000     10,039,000    
Accumulated Depreciation $ (21,000)     (21,000)    
Date of Construction or Acquisition 2015          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 10,039,000          
Deductions during year [Abstract]            
Balance at close of year 21,000          
Multi-Family Residential [Member] | Mariposa - Topeka, KS [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       2,925,000    
Initial Cost to Company [Abstract]            
Land       399,000    
Buildings & Improvements       5,110,000    
Costs capitalized subsequent to acquisition       535,000    
Gross amount at which carried at close of period [Abstract]            
Land       427,000    
Buildings & Improvements       5,617,000    
Total 6,044,000     6,044,000    
Accumulated Depreciation $ (1,498,000)     (1,498,000)    
Date of Construction or Acquisition 2004          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 6,044,000          
Deductions during year [Abstract]            
Balance at close of year 1,498,000          
Multi-Family Residential [Member] | Meadows - Jamestown, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1],[6]       0    
Initial Cost to Company [Abstract]            
Land [6]       590,000    
Buildings & Improvements [6]       4,519,000    
Costs capitalized subsequent to acquisition [6]       1,355,000    
Gross amount at which carried at close of period [Abstract]            
Land [6]       669,000    
Buildings & Improvements [6]       5,795,000    
Total [6] 6,464,000     6,464,000    
Accumulated Depreciation [6] $ (2,135,000)     (2,135,000)    
Date of Construction or Acquisition [6] 1998          
Life on which depreciation in latest income statement is computed [6] 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year [6] $ 6,464,000          
Deductions during year [Abstract]            
Balance at close of year [6] 2,135,000          
Multi-Family Residential [Member] | Monticello Village - Monticello, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       2,956,000    
Initial Cost to Company [Abstract]            
Land       490,000    
Buildings & Improvements       3,756,000    
Costs capitalized subsequent to acquisition       491,000    
Gross amount at which carried at close of period [Abstract]            
Land       621,000    
Buildings & Improvements       4,116,000    
Total 4,737,000     4,737,000    
Accumulated Depreciation $ (1,257,000)     (1,257,000)    
Date of Construction or Acquisition 2004          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 4,737,000          
Deductions during year [Abstract]            
Balance at close of year 1,257,000          
Multi-Family Residential [Member] | Northern Valley - Rochester, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       110,000    
Buildings & Improvements       610,000    
Costs capitalized subsequent to acquisition       129,000    
Gross amount at which carried at close of period [Abstract]            
Land       119,000    
Buildings & Improvements       730,000    
Total 849,000     849,000    
Accumulated Depreciation $ (100,000)     (100,000)    
Date of Construction or Acquisition 2010          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 849,000          
Deductions during year [Abstract]            
Balance at close of year 100,000          
Multi-Family Residential [Member] | North Pointe - Bismarck, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       3,382,000    
Initial Cost to Company [Abstract]            
Land       303,000    
Buildings & Improvements       3,957,000    
Costs capitalized subsequent to acquisition       622,000    
Gross amount at which carried at close of period [Abstract]            
Land       354,000    
Buildings & Improvements       4,528,000    
Total 4,882,000     4,882,000    
Accumulated Depreciation (1,474,000)     (1,474,000)    
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year 4,882,000          
Deductions during year [Abstract]            
Balance at close of year $ 1,474,000          
Multi-Family Residential [Member] | North Pointe - Bismarck, ND [Member] | Minimum [Member]            
Gross amount at which carried at close of period [Abstract]            
Date of Construction or Acquisition 1995          
Life on which depreciation in latest income statement is computed 24 years          
Multi-Family Residential [Member] | North Pointe - Bismarck, ND [Member] | Maximum [Member]            
Gross amount at which carried at close of period [Abstract]            
Date of Construction or Acquisition 2011          
Life on which depreciation in latest income statement is computed 40 years          
Multi-Family Residential [Member] | Northridge - Bismarck, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       6,322,000    
Initial Cost to Company [Abstract]            
Land       884,000    
Buildings & Improvements       7,516,000    
Costs capitalized subsequent to acquisition       26,000    
Gross amount at which carried at close of period [Abstract]            
Land       888,000    
Buildings & Improvements       7,538,000    
Total $ 8,426,000     8,426,000    
Accumulated Depreciation $ (126,000)     (126,000)    
Date of Construction or Acquisition 2014          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 8,426,000          
Deductions during year [Abstract]            
Balance at close of year 126,000          
Multi-Family Residential [Member] | Oakmont Estates - Sioux Falls, SD [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       2,418,000    
Initial Cost to Company [Abstract]            
Land       422,000    
Buildings & Improvements       4,838,000    
Costs capitalized subsequent to acquisition       638,000    
Gross amount at which carried at close of period [Abstract]            
Land       627,000    
Buildings & Improvements       5,271,000    
Total 5,898,000     5,898,000    
Accumulated Depreciation $ (1,746,000)     (1,746,000)    
Date of Construction or Acquisition 2002          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 5,898,000          
Deductions during year [Abstract]            
Balance at close of year 1,746,000          
Multi-Family Residential [Member] | Oakwood Estates - Sioux Falls, SD [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       3,939,000    
Initial Cost to Company [Abstract]            
Land       543,000    
Buildings & Improvements       2,784,000    
Costs capitalized subsequent to acquisition       4,336,000    
Gross amount at which carried at close of period [Abstract]            
Land       777,000    
Buildings & Improvements       6,886,000    
Total 7,663,000     7,663,000    
Accumulated Depreciation $ (3,214,000)     (3,214,000)    
Date of Construction or Acquisition 1993          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 7,663,000          
Deductions during year [Abstract]            
Balance at close of year 3,214,000          
Multi-Family Residential [Member] | Olympic Village - Billings, MT [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       10,575,000    
Initial Cost to Company [Abstract]            
Land       1,164,000    
Buildings & Improvements       10,441,000    
Costs capitalized subsequent to acquisition       3,086,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,785,000    
Buildings & Improvements       12,906,000    
Total 14,691,000     14,691,000    
Accumulated Depreciation $ (4,881,000)     (4,881,000)    
Date of Construction or Acquisition 2000          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 14,691,000          
Deductions during year [Abstract]            
Balance at close of year 4,881,000          
Multi-Family Residential [Member] | Olympik Village - Rochester, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       4,382,000    
Initial Cost to Company [Abstract]            
Land       1,034,000    
Buildings & Improvements       6,109,000    
Costs capitalized subsequent to acquisition       1,968,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,183,000    
Buildings & Improvements       7,928,000    
Total 9,111,000     9,111,000    
Accumulated Depreciation $ (2,127,000)     (2,127,000)    
Date of Construction or Acquisition 2005          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 9,111,000          
Deductions during year [Abstract]            
Balance at close of year 2,127,000          
Multi-Family Residential [Member] | Oxbow Park - Sioux Falls, SD [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       3,846,000    
Initial Cost to Company [Abstract]            
Land       404,000    
Buildings & Improvements       3,152,000    
Costs capitalized subsequent to acquisition       2,894,000    
Gross amount at which carried at close of period [Abstract]            
Land       824,000    
Buildings & Improvements       5,626,000    
Total 6,450,000     6,450,000    
Accumulated Depreciation $ (2,808,000)     (2,808,000)    
Date of Construction or Acquisition 1994          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 6,450,000          
Deductions during year [Abstract]            
Balance at close of year $ 2,808,000          
Multi-Family Residential [Member] | Oxbow Park - Sioux Falls, SD [Member] | Minimum [Member]            
Gross amount at which carried at close of period [Abstract]            
Life on which depreciation in latest income statement is computed 24 years          
Multi-Family Residential [Member] | Oxbow Park - Sioux Falls, SD [Member] | Maximum [Member]            
Gross amount at which carried at close of period [Abstract]            
Life on which depreciation in latest income statement is computed 40 years          
Multi-Family Residential [Member] | Park Meadows - Waite Park, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       8,482,000    
Initial Cost to Company [Abstract]            
Land       1,143,000    
Buildings & Improvements       9,099,000    
Costs capitalized subsequent to acquisition       5,792,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,629,000    
Buildings & Improvements       14,405,000    
Total $ 16,034,000     16,034,000    
Accumulated Depreciation $ (5,939,000)     (5,939,000)    
Date of Construction or Acquisition 1997          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 16,034,000          
Deductions during year [Abstract]            
Balance at close of year 5,939,000          
Multi-Family Residential [Member] | Pebble Springs - Bismarck, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       757,000    
Initial Cost to Company [Abstract]            
Land       7,000    
Buildings & Improvements       748,000    
Costs capitalized subsequent to acquisition       165,000    
Gross amount at which carried at close of period [Abstract]            
Land       54,000    
Buildings & Improvements       866,000    
Total 920,000     920,000    
Accumulated Depreciation $ (349,000)     (349,000)    
Date of Construction or Acquisition 1999          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 920,000          
Deductions during year [Abstract]            
Balance at close of year 349,000          
Multi-Family Residential [Member] | Pinehurst - Billings, MT [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       205,000    
Initial Cost to Company [Abstract]            
Land       72,000    
Buildings & Improvements       687,000    
Costs capitalized subsequent to acquisition       251,000    
Gross amount at which carried at close of period [Abstract]            
Land       81,000    
Buildings & Improvements       929,000    
Total 1,010,000     1,010,000    
Accumulated Depreciation $ (305,000)     (305,000)    
Date of Construction or Acquisition 2002          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,010,000          
Deductions during year [Abstract]            
Balance at close of year 305,000          
Multi-Family Residential [Member] | Pinecone Villas - Sartell, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       584,000    
Buildings & Improvements       2,191,000    
Costs capitalized subsequent to acquisition       27,000    
Gross amount at which carried at close of period [Abstract]            
Land       585,000    
Buildings & Improvements       2,217,000    
Total 2,802,000     2,802,000    
Accumulated Depreciation $ (95,000)     (95,000)    
Date of Construction or Acquisition 2013          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 2,802,000          
Deductions during year [Abstract]            
Balance at close of year 95,000          
Multi-Family Residential [Member] | Pines - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       111,000    
Initial Cost to Company [Abstract]            
Land       35,000    
Buildings & Improvements       215,000    
Costs capitalized subsequent to acquisition       185,000    
Gross amount at which carried at close of period [Abstract]            
Land       49,000    
Buildings & Improvements       386,000    
Total 435,000     435,000    
Accumulated Depreciation $ (141,000)     (141,000)    
Date of Construction or Acquisition 1997          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 435,000          
Deductions during year [Abstract]            
Balance at close of year 141,000          
Multi-Family Residential [Member] | Plaza - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       5,348,000    
Initial Cost to Company [Abstract]            
Land       867,000    
Buildings & Improvements       12,784,000    
Costs capitalized subsequent to acquisition       2,455,000    
Gross amount at which carried at close of period [Abstract]            
Land       995,000    
Buildings & Improvements       15,111,000    
Total 16,106,000     16,106,000    
Accumulated Depreciation $ (2,433,000)     (2,433,000)    
Date of Construction or Acquisition 2009          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 16,106,000          
Deductions during year [Abstract]            
Balance at close of year 2,433,000          
Multi-Family Residential [Member] | Pointe West - Rapid City, SD [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       2,624,000    
Initial Cost to Company [Abstract]            
Land       240,000    
Buildings & Improvements       3,538,000    
Costs capitalized subsequent to acquisition       1,527,000    
Gross amount at which carried at close of period [Abstract]            
Land       368,000    
Buildings & Improvements       4,937,000    
Total 5,305,000     5,305,000    
Accumulated Depreciation $ (2,379,000)     (2,379,000)    
Date of Construction or Acquisition 1994          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 5,305,000          
Deductions during year [Abstract]            
Balance at close of year $ 2,379,000          
Multi-Family Residential [Member] | Pointe West - Rapid City, SD [Member] | Minimum [Member]            
Gross amount at which carried at close of period [Abstract]            
Life on which depreciation in latest income statement is computed 24 years          
Multi-Family Residential [Member] | Pointe West - Rapid City, SD [Member] | Maximum [Member]            
Gross amount at which carried at close of period [Abstract]            
Life on which depreciation in latest income statement is computed 40 years          
Multi-Family Residential [Member] | Ponds at Heritage Place - Sartell, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       3,852,000    
Initial Cost to Company [Abstract]            
Land       395,000    
Buildings & Improvements       4,564,000    
Costs capitalized subsequent to acquisition       320,000    
Gross amount at which carried at close of period [Abstract]            
Land       404,000    
Buildings & Improvements       4,875,000    
Total $ 5,279,000     5,279,000    
Accumulated Depreciation $ (363,000)     (363,000)    
Date of Construction or Acquisition 2012          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 5,279,000          
Deductions during year [Abstract]            
Balance at close of year 363,000          
Multi-Family Residential [Member] | Prairie Winds - Sioux Falls, SD [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       1,410,000    
Initial Cost to Company [Abstract]            
Land       144,000    
Buildings & Improvements       1,816,000    
Costs capitalized subsequent to acquisition       487,000    
Gross amount at which carried at close of period [Abstract]            
Land       235,000    
Buildings & Improvements       2,212,000    
Total 2,447,000     2,447,000    
Accumulated Depreciation $ (1,228,000)     (1,228,000)    
Date of Construction or Acquisition 1993          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 2,447,000          
Deductions during year [Abstract]            
Balance at close of year $ 1,228,000          
Multi-Family Residential [Member] | Prairie Winds - Sioux Falls, SD [Member] | Minimum [Member]            
Gross amount at which carried at close of period [Abstract]            
Life on which depreciation in latest income statement is computed 24 years          
Multi-Family Residential [Member] | Prairie Winds - Sioux Falls, SD [Member] | Maximum [Member]            
Gross amount at which carried at close of period [Abstract]            
Life on which depreciation in latest income statement is computed 40 years          
Multi-Family Residential [Member] | Quarry Ridge - Rochester, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       27,268,000    
Initial Cost to Company [Abstract]            
Land       2,254,000    
Buildings & Improvements       30,024,000    
Costs capitalized subsequent to acquisition       1,392,000    
Gross amount at which carried at close of period [Abstract]            
Land       2,307,000    
Buildings & Improvements       31,363,000    
Total $ 33,670,000     33,670,000    
Accumulated Depreciation $ (4,533,000)     (4,533,000)    
Date of Construction or Acquisition 2006          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 33,670,000          
Deductions during year [Abstract]            
Balance at close of year 4,533,000          
Multi-Family Residential [Member] | RED 20 - Minneapolis, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       1,900,000    
Buildings & Improvements       26,412,000    
Costs capitalized subsequent to acquisition       4,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,900,000    
Buildings & Improvements       26,416,000    
Total 28,316,000     28,316,000    
Accumulated Depreciation $ (445,000)     (445,000)    
Date of Construction or Acquisition 2013          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 28,316,000          
Deductions during year [Abstract]            
Balance at close of year 445,000          
Multi-Family Residential [Member] | Regency Park Estates - St. Cloud, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       6,680,000    
Initial Cost to Company [Abstract]            
Land       702,000    
Buildings & Improvements       10,198,000    
Costs capitalized subsequent to acquisition       1,465,000    
Gross amount at which carried at close of period [Abstract]            
Land       811,000    
Buildings & Improvements       11,554,000    
Total 12,365,000     12,365,000    
Accumulated Depreciation $ (1,162,000)     (1,162,000)    
Date of Construction or Acquisition 2011          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 12,365,000          
Deductions during year [Abstract]            
Balance at close of year 1,162,000          
Multi-Family Residential [Member] | Ridge Oaks - Sioux City, IA [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       3,359,000    
Initial Cost to Company [Abstract]            
Land       178,000    
Buildings & Improvements       4,073,000    
Costs capitalized subsequent to acquisition       2,437,000    
Gross amount at which carried at close of period [Abstract]            
Land       288,000    
Buildings & Improvements       6,400,000    
Total 6,688,000     6,688,000    
Accumulated Depreciation $ (2,205,000)     (2,205,000)    
Date of Construction or Acquisition 2001          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 6,688,000          
Deductions during year [Abstract]            
Balance at close of year 2,205,000          
Multi-Family Residential [Member] | Rimrock West - Billings, MT [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       3,282,000    
Initial Cost to Company [Abstract]            
Land       330,000    
Buildings & Improvements       3,489,000    
Costs capitalized subsequent to acquisition       1,510,000    
Gross amount at which carried at close of period [Abstract]            
Land       435,000    
Buildings & Improvements       4,894,000    
Total 5,329,000     5,329,000    
Accumulated Depreciation $ (1,765,000)     (1,765,000)    
Date of Construction or Acquisition 1999          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 5,329,000          
Deductions during year [Abstract]            
Balance at close of year 1,765,000          
Multi-Family Residential [Member] | River Ridge - Bismarck, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       13,200,000    
Initial Cost to Company [Abstract]            
Land       576,000    
Buildings & Improvements       23,826,000    
Costs capitalized subsequent to acquisition       998,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,438,000    
Buildings & Improvements       23,962,000    
Total 25,400,000     25,400,000    
Accumulated Depreciation $ (1,290,000)     (1,290,000)    
Date of Construction or Acquisition 2008          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 25,400,000          
Deductions during year [Abstract]            
Balance at close of year 1,290,000          
Multi-Family Residential [Member] | Rocky Meadows - Billings, MT [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       5,089,000    
Initial Cost to Company [Abstract]            
Land       656,000    
Buildings & Improvements       5,726,000    
Costs capitalized subsequent to acquisition       1,201,000    
Gross amount at which carried at close of period [Abstract]            
Land       772,000    
Buildings & Improvements       6,811,000    
Total 7,583,000     7,583,000    
Accumulated Depreciation $ (3,129,000)     (3,129,000)    
Date of Construction or Acquisition 1995          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 7,583,000          
Deductions during year [Abstract]            
Balance at close of year 3,129,000          
Multi-Family Residential [Member] | Rum River - Isanti, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       3,536,000    
Initial Cost to Company [Abstract]            
Land       843,000    
Buildings & Improvements       4,823,000    
Costs capitalized subsequent to acquisition       215,000    
Gross amount at which carried at close of period [Abstract]            
Land       862,000    
Buildings & Improvements       5,019,000    
Total 5,881,000     5,881,000    
Accumulated Depreciation $ (1,020,000)     (1,020,000)    
Date of Construction or Acquisition 2007          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 5,881,000          
Deductions during year [Abstract]            
Balance at close of year 1,020,000          
Multi-Family Residential [Member] | Sherwood - Topeka, KS [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       12,134,000    
Initial Cost to Company [Abstract]            
Land       1,142,000    
Buildings & Improvements       14,684,000    
Costs capitalized subsequent to acquisition       3,064,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,694,000    
Buildings & Improvements       17,196,000    
Total 18,890,000     18,890,000    
Accumulated Depreciation $ (6,619,000)     (6,619,000)    
Date of Construction or Acquisition 1999          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 18,890,000          
Deductions during year [Abstract]            
Balance at close of year 6,619,000          
Multi-Family Residential [Member] | Sierra Vista - Sioux Falls, SD [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       1,390,000    
Initial Cost to Company [Abstract]            
Land       241,000    
Buildings & Improvements       2,097,000    
Costs capitalized subsequent to acquisition       435,000    
Gross amount at which carried at close of period [Abstract]            
Land       265,000    
Buildings & Improvements       2,508,000    
Total 2,773,000     2,773,000    
Accumulated Depreciation $ (273,000)     (273,000)    
Date of Construction or Acquisition 2011          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 2,773,000          
Deductions during year [Abstract]            
Balance at close of year 273,000          
Multi-Family Residential [Member] | Silver Springs - Rapid City, SD [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       2,230,000    
Initial Cost to Company [Abstract]            
Land       215,000    
Buildings & Improvements       3,006,000    
Costs capitalized subsequent to acquisition       48,000    
Gross amount at which carried at close of period [Abstract]            
Land       215,000    
Buildings & Improvements       3,054,000    
Total 3,269,000     3,269,000    
Accumulated Depreciation $ (68,000)     (68,000)    
Date of Construction or Acquisition 2014          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 3,269,000          
Deductions during year [Abstract]            
Balance at close of year 68,000          
Multi-Family Residential [Member] | South Pointe - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       8,613,000    
Initial Cost to Company [Abstract]            
Land       550,000    
Buildings & Improvements       9,548,000    
Costs capitalized subsequent to acquisition       2,847,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,343,000    
Buildings & Improvements       11,602,000    
Total 12,945,000     12,945,000    
Accumulated Depreciation $ (5,494,000)     (5,494,000)    
Date of Construction or Acquisition 1995          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 12,945,000          
Deductions during year [Abstract]            
Balance at close of year $ 5,494,000          
Multi-Family Residential [Member] | South Pointe - Minot, ND [Member] | Minimum [Member]            
Gross amount at which carried at close of period [Abstract]            
Life on which depreciation in latest income statement is computed 24 years          
Multi-Family Residential [Member] | South Pointe - Minot, ND [Member] | Maximum [Member]            
Gross amount at which carried at close of period [Abstract]            
Life on which depreciation in latest income statement is computed 40 years          
Multi-Family Residential [Member] | Southpoint - Grand Forks, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1],[6]       0    
Initial Cost to Company [Abstract]            
Land [6]       576,000    
Buildings & Improvements [6]       9,893,000    
Costs capitalized subsequent to acquisition [6]       48,000    
Gross amount at which carried at close of period [Abstract]            
Land [6]       591,000    
Buildings & Improvements [6]       9,926,000    
Total [6] $ 10,517,000     10,517,000    
Accumulated Depreciation [6] $ (414,000)     (414,000)    
Date of Construction or Acquisition [6] 2013          
Life on which depreciation in latest income statement is computed [6] 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year [6] $ 10,517,000          
Deductions during year [Abstract]            
Balance at close of year [6] 414,000          
Multi-Family Residential [Member] | Southview - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       1,035,000    
Initial Cost to Company [Abstract]            
Land       185,000    
Buildings & Improvements       469,000    
Costs capitalized subsequent to acquisition       410,000    
Gross amount at which carried at close of period [Abstract]            
Land       240,000    
Buildings & Improvements       824,000    
Total 1,064,000     1,064,000    
Accumulated Depreciation $ (371,000)     (371,000)    
Date of Construction or Acquisition 1994          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,064,000          
Deductions during year [Abstract]            
Balance at close of year 371,000          
Multi-Family Residential [Member] | Southwind - Grand Forks, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       5,503,000    
Initial Cost to Company [Abstract]            
Land       400,000    
Buildings & Improvements       5,034,000    
Costs capitalized subsequent to acquisition       2,974,000    
Gross amount at which carried at close of period [Abstract]            
Land       765,000    
Buildings & Improvements       7,643,000    
Total 8,408,000     8,408,000    
Accumulated Depreciation $ (3,486,000)     (3,486,000)    
Date of Construction or Acquisition 1995          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 8,408,000          
Deductions during year [Abstract]            
Balance at close of year $ 3,486,000          
Multi-Family Residential [Member] | Southwind - Grand Forks, ND [Member] | Minimum [Member]            
Gross amount at which carried at close of period [Abstract]            
Life on which depreciation in latest income statement is computed 24 years          
Multi-Family Residential [Member] | Southwind - Grand Forks, ND [Member] | Maximum [Member]            
Gross amount at which carried at close of period [Abstract]            
Life on which depreciation in latest income statement is computed 40 years          
Multi-Family Residential [Member] | Summit Park - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       963,000    
Initial Cost to Company [Abstract]            
Land       161,000    
Buildings & Improvements       1,898,000    
Costs capitalized subsequent to acquisition       1,550,000    
Gross amount at which carried at close of period [Abstract]            
Land       560,000    
Buildings & Improvements       3,049,000    
Total $ 3,609,000     3,609,000    
Accumulated Depreciation $ (1,249,000)     (1,249,000)    
Date of Construction or Acquisition 1997          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 3,609,000          
Deductions during year [Abstract]            
Balance at close of year $ 1,249,000          
Multi-Family Residential [Member] | Summit Park - Minot, ND [Member] | Minimum [Member]            
Gross amount at which carried at close of period [Abstract]            
Life on which depreciation in latest income statement is computed 24 years          
Multi-Family Residential [Member] | Summit Park - Minot, ND [Member] | Maximum [Member]            
Gross amount at which carried at close of period [Abstract]            
Life on which depreciation in latest income statement is computed 40 years          
Multi-Family Residential [Member] | Sunset Trail - Rochester, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       8,009,000    
Initial Cost to Company [Abstract]            
Land       336,000    
Buildings & Improvements       12,814,000    
Costs capitalized subsequent to acquisition       2,652,000    
Gross amount at which carried at close of period [Abstract]            
Land       581,000    
Buildings & Improvements       15,221,000    
Total $ 15,802,000     15,802,000    
Accumulated Depreciation $ (5,453,000)     (5,453,000)    
Date of Construction or Acquisition 1999          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 15,802,000          
Deductions during year [Abstract]            
Balance at close of year 5,453,000          
Multi-Family Residential [Member] | Temple - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       75,000    
Initial Cost to Company [Abstract]            
Land       0    
Buildings & Improvements       0    
Costs capitalized subsequent to acquisition       231,000    
Gross amount at which carried at close of period [Abstract]            
Land       0    
Buildings & Improvements       231,000    
Total 231,000     231,000    
Accumulated Depreciation $ (57,000)     (57,000)    
Date of Construction or Acquisition 2006          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 231,000          
Deductions during year [Abstract]            
Balance at close of year 57,000          
Multi-Family Residential [Member] | Terrace Heights - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       160,000    
Initial Cost to Company [Abstract]            
Land       29,000    
Buildings & Improvements       312,000    
Costs capitalized subsequent to acquisition       142,000    
Gross amount at which carried at close of period [Abstract]            
Land       40,000    
Buildings & Improvements       443,000    
Total 483,000     483,000    
Accumulated Depreciation $ (172,000)     (172,000)    
Date of Construction or Acquisition 2006          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 483,000          
Deductions during year [Abstract]            
Balance at close of year 172,000          
Multi-Family Residential [Member] | Thomasbrook - Lincoln, NE [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       5,893,000    
Initial Cost to Company [Abstract]            
Land       600,000    
Buildings & Improvements       10,306,000    
Costs capitalized subsequent to acquisition       3,336,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,403,000    
Buildings & Improvements       12,839,000    
Total 14,242,000     14,242,000    
Accumulated Depreciation $ (4,680,000)     (4,680,000)    
Date of Construction or Acquisition 1999          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 14,242,000          
Deductions during year [Abstract]            
Balance at close of year 4,680,000          
Multi-Family Residential [Member] | University Park Place - St. Cloud, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       78,000    
Buildings & Improvements       450,000    
Costs capitalized subsequent to acquisition       115,000    
Gross amount at which carried at close of period [Abstract]            
Land       83,000    
Buildings & Improvements       560,000    
Total 643,000     643,000    
Accumulated Depreciation $ (118,000)     (118,000)    
Date of Construction or Acquisition 2007          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 643,000          
Deductions during year [Abstract]            
Balance at close of year 118,000          
Multi-Family Residential [Member] | Valley Park - Grand Forks, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       3,822,000    
Initial Cost to Company [Abstract]            
Land       294,000    
Buildings & Improvements       4,137,000    
Costs capitalized subsequent to acquisition       3,508,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,115,000    
Buildings & Improvements       6,824,000    
Total 7,939,000     7,939,000    
Accumulated Depreciation $ (2,599,000)     (2,599,000)    
Date of Construction or Acquisition 1999          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 7,939,000          
Deductions during year [Abstract]            
Balance at close of year 2,599,000          
Multi-Family Residential [Member] | Villa West - Topeka, KS [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       12,106,000    
Initial Cost to Company [Abstract]            
Land       1,590,000    
Buildings & Improvements       15,760,000    
Costs capitalized subsequent to acquisition       923,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,876,000    
Buildings & Improvements       16,397,000    
Total 18,273,000     18,273,000    
Accumulated Depreciation $ (1,331,000)     (1,331,000)    
Date of Construction or Acquisition 2012          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 18,273,000          
Deductions during year [Abstract]            
Balance at close of year 1,331,000          
Multi-Family Residential [Member] | Village Green - Rochester, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       1,047,000    
Initial Cost to Company [Abstract]            
Land       234,000    
Buildings & Improvements       2,296,000    
Costs capitalized subsequent to acquisition       962,000    
Gross amount at which carried at close of period [Abstract]            
Land       359,000    
Buildings & Improvements       3,133,000    
Total 3,492,000     3,492,000    
Accumulated Depreciation $ (935,000)     (935,000)    
Date of Construction or Acquisition 2003          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 3,492,000          
Deductions during year [Abstract]            
Balance at close of year 935,000          
Multi-Family Residential [Member] | West Stonehill - Waite Park, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       8,448,000    
Initial Cost to Company [Abstract]            
Land       939,000    
Buildings & Improvements       10,167,000    
Costs capitalized subsequent to acquisition       5,224,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,533,000    
Buildings & Improvements       14,797,000    
Total 16,330,000     16,330,000    
Accumulated Depreciation $ (6,896,000)     (6,896,000)    
Date of Construction or Acquisition 1995          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 16,330,000          
Deductions during year [Abstract]            
Balance at close of year 6,896,000          
Multi-Family Residential [Member] | Westridge - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       1,604,000    
Initial Cost to Company [Abstract]            
Land       68,000    
Buildings & Improvements       1,887,000    
Costs capitalized subsequent to acquisition       263,000    
Gross amount at which carried at close of period [Abstract]            
Land       77,000    
Buildings & Improvements       2,141,000    
Total 2,218,000     2,218,000    
Accumulated Depreciation $ (377,000)     (377,000)    
Date of Construction or Acquisition 2008          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 2,218,000          
Deductions during year [Abstract]            
Balance at close of year 377,000          
Multi-Family Residential [Member] | Westwood Park - Bismarck, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       1,950,000    
Initial Cost to Company [Abstract]            
Land       116,000    
Buildings & Improvements       1,909,000    
Costs capitalized subsequent to acquisition       1,784,000    
Gross amount at which carried at close of period [Abstract]            
Land       284,000    
Buildings & Improvements       3,525,000    
Total 3,809,000     3,809,000    
Accumulated Depreciation $ (1,425,000)     (1,425,000)    
Date of Construction or Acquisition 1998          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 3,809,000          
Deductions during year [Abstract]            
Balance at close of year 1,425,000          
Multi-Family Residential [Member] | Whispering Ridge - Omaha, NE [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       22,000,000    
Initial Cost to Company [Abstract]            
Land       2,139,000    
Buildings & Improvements       25,424,000    
Costs capitalized subsequent to acquisition       732,000    
Gross amount at which carried at close of period [Abstract]            
Land       2,276,000    
Buildings & Improvements       26,019,000    
Total 28,295,000     28,295,000    
Accumulated Depreciation $ (1,563,000)     (1,563,000)    
Date of Construction or Acquisition 2012          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 28,295,000          
Deductions during year [Abstract]            
Balance at close of year 1,563,000          
Multi-Family Residential [Member] | Williston Garden - Williston, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       10,870,000    
Initial Cost to Company [Abstract]            
Land       1,400,000    
Buildings & Improvements       17,696,000    
Costs capitalized subsequent to acquisition       85,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,421,000    
Buildings & Improvements       17,760,000    
Total 19,181,000     19,181,000    
Accumulated Depreciation $ (2,132,000)     (2,132,000)    
Date of Construction or Acquisition 2012          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 19,181,000          
Deductions during year [Abstract]            
Balance at close of year 2,132,000          
Multi-Family Residential [Member] | Winchester - Rochester, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       2,564,000    
Initial Cost to Company [Abstract]            
Land       748,000    
Buildings & Improvements       5,622,000    
Costs capitalized subsequent to acquisition       1,846,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,009,000    
Buildings & Improvements       7,207,000    
Total 8,216,000     8,216,000    
Accumulated Depreciation $ (2,297,000)     (2,297,000)    
Date of Construction or Acquisition 2003          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 8,216,000          
Deductions during year [Abstract]            
Balance at close of year 2,297,000          
Multi-Family Residential [Member] | Woodridge - Rochester, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       6,257,000    
Initial Cost to Company [Abstract]            
Land       370,000    
Buildings & Improvements       6,028,000    
Costs capitalized subsequent to acquisition       2,207,000    
Gross amount at which carried at close of period [Abstract]            
Land       642,000    
Buildings & Improvements       7,963,000    
Total 8,605,000     8,605,000    
Accumulated Depreciation $ (3,557,000)     (3,557,000)    
Date of Construction or Acquisition 1997          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 8,605,000          
Deductions during year [Abstract]            
Balance at close of year 3,557,000          
Multi-Family Residential [Member] | Renaissance Heights - Williston ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       2,464,000    
Buildings & Improvements       43,488,000    
Costs capitalized subsequent to acquisition       123,000    
Gross amount at which carried at close of period [Abstract]            
Land       2,467,000    
Buildings & Improvements       43,608,000    
Total 46,075,000     46,075,000    
Accumulated Depreciation $ (848,000)     (848,000)    
Date of Construction or Acquisition 2013          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 46,075,000          
Deductions during year [Abstract]            
Balance at close of year 848,000          
Multi-Family Residential [Member] | Wholly Owned Properties [Member]            
Reconciliations of total real estate carrying value [Abstract]            
Additions 183,114,000 84,117,000 113,859,000      
Commercial Healthcare [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       220,070,000    
Initial Cost to Company [Abstract]            
Land       33,522,000    
Buildings & Improvements       409,346,000    
Costs capitalized subsequent to acquisition       52,153,000    
Gross amount at which carried at close of period [Abstract]            
Land       34,201,000    
Buildings & Improvements       460,820,000    
Total 495,021,000     495,021,000    
Accumulated Depreciation (112,515,000)     (112,515,000)    
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year 495,021,000          
Deductions during year [Abstract]            
Balance at close of year 112,515,000          
Commercial Healthcare [Member] | 2800 Medical Building - Minneapolis, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       7,740,000    
Initial Cost to Company [Abstract]            
Land       204,000    
Buildings & Improvements       7,135,000    
Costs capitalized subsequent to acquisition       2,492,000    
Gross amount at which carried at close of period [Abstract]            
Land       229,000    
Buildings & Improvements       9,602,000    
Total 9,831,000     9,831,000    
Accumulated Depreciation $ (3,037,000)     (3,037,000)    
Date of Construction or Acquisition 2005          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 9,831,000          
Deductions during year [Abstract]            
Balance at close of year 3,037,000          
Commercial Healthcare [Member] | 2828 Chicago Avenue - Minneapolis, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       12,105,000    
Initial Cost to Company [Abstract]            
Land       726,000    
Buildings & Improvements       11,319,000    
Costs capitalized subsequent to acquisition       5,627,000    
Gross amount at which carried at close of period [Abstract]            
Land       729,000    
Buildings & Improvements       16,943,000    
Total 17,672,000     17,672,000    
Accumulated Depreciation $ (4,011,000)     (4,011,000)    
Date of Construction or Acquisition 2007          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 17,672,000          
Deductions during year [Abstract]            
Balance at close of year 4,011,000          
Commercial Healthcare [Member] | Airport Medical - Bloomington, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       431,000    
Initial Cost to Company [Abstract]            
Land       0    
Buildings & Improvements       4,678,000    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       0    
Buildings & Improvements       4,678,000    
Total 4,678,000     4,678,000    
Accumulated Depreciation $ (1,730,000)     (1,730,000)    
Date of Construction or Acquisition 2002          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 4,678,000          
Deductions during year [Abstract]            
Balance at close of year 1,730,000          
Commercial Healthcare [Member] | Billings 2300 Grant Road - Billings, MT [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       1,226,000    
Initial Cost to Company [Abstract]            
Land       649,000    
Buildings & Improvements       1,216,000    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       649,000    
Buildings & Improvements       1,216,000    
Total 1,865,000     1,865,000    
Accumulated Depreciation $ (146,000)     (146,000)    
Date of Construction or Acquisition 2010          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,865,000          
Deductions during year [Abstract]            
Balance at close of year 146,000          
Commercial Healthcare [Member] | Burnsville 303 Nicollet Medical (Ridgeview) - Burnsville, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       8,092,000    
Initial Cost to Company [Abstract]            
Land       1,071,000    
Buildings & Improvements       6,842,000    
Costs capitalized subsequent to acquisition       1,968,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,092,000    
Buildings & Improvements       8,789,000    
Total 9,881,000     9,881,000    
Accumulated Depreciation $ (1,612,000)     (1,612,000)    
Date of Construction or Acquisition 2008          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 9,881,000          
Deductions during year [Abstract]            
Balance at close of year 1,612,000          
Commercial Healthcare [Member] | Burnsville 305 Nicollet Medical (Ridgeview South) - Burnsville, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       5,066,000    
Initial Cost to Company [Abstract]            
Land       189,000    
Buildings & Improvements       5,127,000    
Costs capitalized subsequent to acquisition       971,000    
Gross amount at which carried at close of period [Abstract]            
Land       203,000    
Buildings & Improvements       6,084,000    
Total 6,287,000     6,287,000    
Accumulated Depreciation $ (1,078,000)     (1,078,000)    
Date of Construction or Acquisition 2008          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 6,287,000          
Deductions during year [Abstract]            
Balance at close of year 1,078,000          
Commercial Healthcare [Member] | Casper 1930 E 12th Street (Park Place) - Casper, WY [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1],[6]       0    
Initial Cost to Company [Abstract]            
Land [6]       439,000    
Buildings & Improvements [6]       5,780,000    
Costs capitalized subsequent to acquisition [6]       172,000    
Gross amount at which carried at close of period [Abstract]            
Land [6]       439,000    
Buildings & Improvements [6]       5,952,000    
Total [6] 6,391,000     6,391,000    
Accumulated Depreciation [6] $ (855,000)     (855,000)    
Date of Construction or Acquisition [6] 2009          
Life on which depreciation in latest income statement is computed [6] 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year [6] $ 6,391,000          
Deductions during year [Abstract]            
Balance at close of year [6] 855,000          
Commercial Healthcare [Member] | Casper 3955 E 12th Street (Meadow Wind) - Casper, WY [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1],[6]       0    
Initial Cost to Company [Abstract]            
Land [6]       388,000    
Buildings & Improvements [6]       10,494,000    
Costs capitalized subsequent to acquisition [6]       576,000    
Gross amount at which carried at close of period [Abstract]            
Land [6]       459,000    
Buildings & Improvements [6]       10,999,000    
Total [6] 11,458,000     11,458,000    
Accumulated Depreciation [6] $ (1,510,000)     (1,510,000)    
Date of Construction or Acquisition [6] 2009          
Life on which depreciation in latest income statement is computed [6] 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year [6] $ 11,458,000          
Deductions during year [Abstract]            
Balance at close of year [6] 1,510,000          
Commercial Healthcare [Member] | Cheyenne 4010 N College Drive (Aspen Wind) - Cheyenne, WY [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1],[6]       0    
Initial Cost to Company [Abstract]            
Land [6]       628,000    
Buildings & Improvements [6]       10,272,000    
Costs capitalized subsequent to acquisition [6]       270,000    
Gross amount at which carried at close of period [Abstract]            
Land [6]       629,000    
Buildings & Improvements [6]       10,541,000    
Total [6] 11,170,000     11,170,000    
Accumulated Depreciation [6] $ (1,457,000)     (1,457,000)    
Date of Construction or Acquisition [6] 2009          
Life on which depreciation in latest income statement is computed [6] 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year [6] $ 11,170,000          
Deductions during year [Abstract]            
Balance at close of year [6] 1,457,000          
Commercial Healthcare [Member] | Cheyenne 4606 N College Drive (Sierra Hills) - Cheyenne, WY [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1],[6]       0    
Initial Cost to Company [Abstract]            
Land [6]       695,000    
Buildings & Improvements [6]       7,455,000    
Costs capitalized subsequent to acquisition [6]       50,000    
Gross amount at which carried at close of period [Abstract]            
Land [6]       695,000    
Buildings & Improvements [6]       7,505,000    
Total [6] 8,200,000     8,200,000    
Accumulated Depreciation [6] $ (1,020,000)     (1,020,000)    
Date of Construction or Acquisition [6] 2009          
Life on which depreciation in latest income statement is computed [6] 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year [6] $ 8,200,000          
Deductions during year [Abstract]            
Balance at close of year [6] 1,020,000          
Commercial Healthcare [Member] | Denfeld Clinic - Duluth, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       1,430,000    
Initial Cost to Company [Abstract]            
Land       501,000    
Buildings & Improvements       2,597,000    
Costs capitalized subsequent to acquisition       1,000    
Gross amount at which carried at close of period [Abstract]            
Land       501,000    
Buildings & Improvements       2,598,000    
Total 3,099,000     3,099,000    
Accumulated Depreciation $ (718,000)     (718,000)    
Date of Construction or Acquisition 2004          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 3,099,000          
Deductions during year [Abstract]            
Balance at close of year 718,000          
Commercial Healthcare [Member] | Eagan 1440 Duckwood Medical - Eagan, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       521,000    
Buildings & Improvements       1,547,000    
Costs capitalized subsequent to acquisition       556,000    
Gross amount at which carried at close of period [Abstract]            
Land       521,000    
Buildings & Improvements       2,103,000    
Total 2,624,000     2,624,000    
Accumulated Depreciation $ (635,000)     (635,000)    
Date of Construction or Acquisition 2008          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 2,624,000          
Deductions during year [Abstract]            
Balance at close of year 635,000          
Commercial Healthcare [Member] | Edgewood Vista - Belgrade, MT [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       35,000    
Buildings & Improvements       779,000    
Costs capitalized subsequent to acquisition       21,000    
Gross amount at which carried at close of period [Abstract]            
Land       35,000    
Buildings & Improvements       800,000    
Total 835,000     835,000    
Accumulated Depreciation $ (140,000)     (140,000)    
Date of Construction or Acquisition 2008          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 835,000          
Deductions during year [Abstract]            
Balance at close of year 140,000          
Commercial Healthcare [Member] | Edgewood Vista - Billings, MT [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       1,785,000    
Initial Cost to Company [Abstract]            
Land       115,000    
Buildings & Improvements       1,767,000    
Costs capitalized subsequent to acquisition       66,000    
Gross amount at which carried at close of period [Abstract]            
Land       115,000    
Buildings & Improvements       1,833,000    
Total 1,948,000     1,948,000    
Accumulated Depreciation $ (323,000)     (323,000)    
Date of Construction or Acquisition 2008          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,948,000          
Deductions during year [Abstract]            
Balance at close of year 323,000          
Commercial Healthcare [Member] | Edgewood Vista - Bismarck, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       511,000    
Buildings & Improvements       9,193,000    
Costs capitalized subsequent to acquisition       177,000    
Gross amount at which carried at close of period [Abstract]            
Land       511,000    
Buildings & Improvements       9,370,000    
Total 9,881,000     9,881,000    
Accumulated Depreciation $ (2,231,000)     (2,231,000)    
Date of Construction or Acquisition 2005          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 9,881,000          
Deductions during year [Abstract]            
Balance at close of year 2,231,000          
Commercial Healthcare [Member] | Edgewood Vista - Brainerd, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       587,000    
Buildings & Improvements       8,999,000    
Costs capitalized subsequent to acquisition       134,000    
Gross amount at which carried at close of period [Abstract]            
Land       587,000    
Buildings & Improvements       9,133,000    
Total 9,720,000     9,720,000    
Accumulated Depreciation $ (2,184,000)     (2,184,000)    
Date of Construction or Acquisition 2005          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 9,720,000          
Deductions during year [Abstract]            
Balance at close of year 2,184,000          
Commercial Healthcare [Member] | Edgewood Vista - Columbus, NE [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       43,000    
Buildings & Improvements       824,000    
Costs capitalized subsequent to acquisition       24,000    
Gross amount at which carried at close of period [Abstract]            
Land       44,000    
Buildings & Improvements       847,000    
Total 891,000     891,000    
Accumulated Depreciation $ (148,000)     (148,000)    
Date of Construction or Acquisition 2008          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 891,000          
Deductions during year [Abstract]            
Balance at close of year 148,000          
Commercial Healthcare [Member] | Edgewood Vista - East Grand Forks, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       2,718,000    
Initial Cost to Company [Abstract]            
Land       290,000    
Buildings & Improvements       1,352,000    
Costs capitalized subsequent to acquisition       59,000    
Gross amount at which carried at close of period [Abstract]            
Land       290,000    
Buildings & Improvements       1,411,000    
Total 1,701,000     1,701,000    
Accumulated Depreciation $ (251,000)     (251,000)    
Date of Construction or Acquisition 2000          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,701,000          
Deductions during year [Abstract]            
Balance at close of year 251,000          
Commercial Healthcare [Member] | Edgewood Vista - Fargo, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       11,846,000    
Initial Cost to Company [Abstract]            
Land       775,000    
Buildings & Improvements       20,870,000    
Costs capitalized subsequent to acquisition       199,000    
Gross amount at which carried at close of period [Abstract]            
Land       775,000    
Buildings & Improvements       21,069,000    
Total 21,844,000     21,844,000    
Accumulated Depreciation $ (3,730,000)     (3,730,000)    
Date of Construction or Acquisition 2008          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 21,844,000          
Deductions during year [Abstract]            
Balance at close of year 3,730,000          
Commercial Healthcare [Member] | Edgewood Vista - Fremont, NE [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       550,000    
Initial Cost to Company [Abstract]            
Land       56,000    
Buildings & Improvements       490,000    
Costs capitalized subsequent to acquisition       54,000    
Gross amount at which carried at close of period [Abstract]            
Land       56,000    
Buildings & Improvements       544,000    
Total 600,000     600,000    
Accumulated Depreciation $ (179,000)     (179,000)    
Date of Construction or Acquisition 2008          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 600,000          
Deductions during year [Abstract]            
Balance at close of year 179,000          
Commercial Healthcare [Member] | Edgewood Vista - Grand Island, NE [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       33,000    
Buildings & Improvements       773,000    
Costs capitalized subsequent to acquisition       51,000    
Gross amount at which carried at close of period [Abstract]            
Land       39,000    
Buildings & Improvements       818,000    
Total 857,000     857,000    
Accumulated Depreciation $ (142,000)     (142,000)    
Date of Construction or Acquisition 2008          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 857,000          
Deductions during year [Abstract]            
Balance at close of year 142,000          
Commercial Healthcare [Member] | Edgewood Vista - Hastings, NE [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       567,000    
Initial Cost to Company [Abstract]            
Land       49,000    
Buildings & Improvements       517,000    
Costs capitalized subsequent to acquisition       63,000    
Gross amount at which carried at close of period [Abstract]            
Land       50,000    
Buildings & Improvements       579,000    
Total 629,000     629,000    
Accumulated Depreciation $ (197,000)     (197,000)    
Date of Construction or Acquisition 2008          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 629,000          
Deductions during year [Abstract]            
Balance at close of year 197,000          
Commercial Healthcare [Member] | Edgewood Vista - Hermantown I, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       15,197,000    
Initial Cost to Company [Abstract]            
Land       288,000    
Buildings & Improvements       9,871,000    
Costs capitalized subsequent to acquisition       1,761,000    
Gross amount at which carried at close of period [Abstract]            
Land       288,000    
Buildings & Improvements       11,632,000    
Total 11,920,000     11,920,000    
Accumulated Depreciation $ (3,888,000)     (3,888,000)    
Date of Construction or Acquisition 2000          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 11,920,000          
Deductions during year [Abstract]            
Balance at close of year 3,888,000          
Commercial Healthcare [Member] | Edgewood Vista - Hermantown II, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       719,000    
Buildings & Improvements       10,517,000    
Costs capitalized subsequent to acquisition       121,000    
Gross amount at which carried at close of period [Abstract]            
Land       719,000    
Buildings & Improvements       10,638,000    
Total 11,357,000     11,357,000    
Accumulated Depreciation $ (2,542,000)     (2,542,000)    
Date of Construction or Acquisition 2005          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 11,357,000          
Deductions during year [Abstract]            
Balance at close of year 2,542,000          
Commercial Healthcare [Member] | Edgewood Vista - Kalispell, MT [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       568,000    
Initial Cost to Company [Abstract]            
Land       70,000    
Buildings & Improvements       502,000    
Costs capitalized subsequent to acquisition       633,000    
Gross amount at which carried at close of period [Abstract]            
Land       70,000    
Buildings & Improvements       1,135,000    
Total 1,205,000     1,205,000    
Accumulated Depreciation $ (364,000)     (364,000)    
Date of Construction or Acquisition 2001          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,205,000          
Deductions during year [Abstract]            
Balance at close of year 364,000          
Commercial Healthcare [Member] | Edgewood Vista - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       9,017,000    
Initial Cost to Company [Abstract]            
Land       1,045,000    
Buildings & Improvements       11,590,000    
Costs capitalized subsequent to acquisition       210,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,047,000    
Buildings & Improvements       11,798,000    
Total 12,845,000     12,845,000    
Accumulated Depreciation $ (1,307,000)     (1,307,000)    
Date of Construction or Acquisition 2010          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 12,845,000          
Deductions during year [Abstract]            
Balance at close of year 1,307,000          
Commercial Healthcare [Member] | Edgewood Vista - Missoula, MT [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       807,000    
Initial Cost to Company [Abstract]            
Land       109,000    
Buildings & Improvements       854,000    
Costs capitalized subsequent to acquisition       94,000    
Gross amount at which carried at close of period [Abstract]            
Land       116,000    
Buildings & Improvements       941,000    
Total 1,057,000     1,057,000    
Accumulated Depreciation $ (412,000)     (412,000)    
Date of Construction or Acquisition 1996          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,057,000          
Deductions during year [Abstract]            
Balance at close of year 412,000          
Commercial Healthcare [Member] | Edgewood Vista - Norfolk, NE [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       42,000    
Buildings & Improvements       722,000    
Costs capitalized subsequent to acquisition       22,000    
Gross amount at which carried at close of period [Abstract]            
Land       42,000    
Buildings & Improvements       744,000    
Total 786,000     786,000    
Accumulated Depreciation $ (131,000)     (131,000)    
Date of Construction or Acquisition 2008          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 786,000          
Deductions during year [Abstract]            
Balance at close of year 131,000          
Commercial Healthcare [Member] | Edgewood Vista - Omaha, NE [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       359,000    
Initial Cost to Company [Abstract]            
Land       89,000    
Buildings & Improvements       547,000    
Costs capitalized subsequent to acquisition       53,000    
Gross amount at which carried at close of period [Abstract]            
Land       89,000    
Buildings & Improvements       600,000    
Total 689,000     689,000    
Accumulated Depreciation $ (201,000)     (201,000)    
Date of Construction or Acquisition 2001          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 689,000          
Deductions during year [Abstract]            
Balance at close of year 201,000          
Commercial Healthcare [Member] | Edgewood Vista - Sioux Falls, SD [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       1,022,000    
Initial Cost to Company [Abstract]            
Land       314,000    
Buildings & Improvements       974,000    
Costs capitalized subsequent to acquisition       58,000    
Gross amount at which carried at close of period [Abstract]            
Land       314,000    
Buildings & Improvements       1,032,000    
Total 1,346,000     1,346,000    
Accumulated Depreciation $ (185,000)     (185,000)    
Date of Construction or Acquisition 2008          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,346,000          
Deductions during year [Abstract]            
Balance at close of year 185,000          
Commercial Healthcare [Member] | Edgewood Vista - Spearfish, SD [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       315,000    
Buildings & Improvements       8,584,000    
Costs capitalized subsequent to acquisition       124,000    
Gross amount at which carried at close of period [Abstract]            
Land       330,000    
Buildings & Improvements       8,693,000    
Total 9,023,000     9,023,000    
Accumulated Depreciation $ (1,710,000)     (1,710,000)    
Date of Construction or Acquisition 2005          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 9,023,000          
Deductions during year [Abstract]            
Balance at close of year 1,710,000          
Commercial Healthcare [Member] | Edgewood Vista - Virginia, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       12,927,000    
Initial Cost to Company [Abstract]            
Land       246,000    
Buildings & Improvements       11,823,000    
Costs capitalized subsequent to acquisition       313,000    
Gross amount at which carried at close of period [Abstract]            
Land       246,000    
Buildings & Improvements       12,136,000    
Total 12,382,000     12,382,000    
Accumulated Depreciation $ (3,669,000)     (3,669,000)    
Date of Construction or Acquisition 2002          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 12,382,000          
Deductions during year [Abstract]            
Balance at close of year 3,669,000          
Commercial Healthcare [Member] | Edina 6363 France Medical - Edina, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       9,567,000    
Initial Cost to Company [Abstract]            
Land       0    
Buildings & Improvements       12,675,000    
Costs capitalized subsequent to acquisition       2,906,000    
Gross amount at which carried at close of period [Abstract]            
Land       0    
Buildings & Improvements       15,581,000    
Total 15,581,000     15,581,000    
Accumulated Depreciation $ (3,781,000)     (3,781,000)    
Date of Construction or Acquisition 2008          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 15,581,000          
Deductions during year [Abstract]            
Balance at close of year 3,781,000          
Commercial Healthcare [Member] | Edina 6405 France Medical - Edina, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       8,145,000    
Initial Cost to Company [Abstract]            
Land       0    
Buildings & Improvements       12,201,000    
Costs capitalized subsequent to acquisition       41,000    
Gross amount at which carried at close of period [Abstract]            
Land       0    
Buildings & Improvements       12,242,000    
Total 12,242,000     12,242,000    
Accumulated Depreciation $ (2,969,000)     (2,969,000)    
Date of Construction or Acquisition 2008          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 12,242,000          
Deductions during year [Abstract]            
Balance at close of year 2,969,000          
Commercial Healthcare [Member] | Edina 6517 Drew Avenue - Edina, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       353,000    
Buildings & Improvements       660,000    
Costs capitalized subsequent to acquisition       529,000    
Gross amount at which carried at close of period [Abstract]            
Land       372,000    
Buildings & Improvements       1,170,000    
Total 1,542,000     1,542,000    
Accumulated Depreciation $ (579,000)     (579,000)    
Date of Construction or Acquisition 2002          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,542,000          
Deductions during year [Abstract]            
Balance at close of year 579,000          
Commercial Healthcare [Member] | Edina 6525 Drew Avenue - Edina, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       388,000    
Buildings & Improvements       117,000    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       388,000    
Buildings & Improvements       117,000    
Total 505,000     505,000    
Accumulated Depreciation $ (10,000)     (10,000)    
Date of Construction or Acquisition 2011          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 505,000          
Deductions during year [Abstract]            
Balance at close of year 10,000          
Commercial Healthcare [Member] | Edina 6525 France SMC II - Edina, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       9,803,000    
Initial Cost to Company [Abstract]            
Land       755,000    
Buildings & Improvements       8,054,000    
Costs capitalized subsequent to acquisition       5,723,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,040,000    
Buildings & Improvements       13,492,000    
Total 14,532,000     14,532,000    
Accumulated Depreciation $ (5,874,000)     (5,874,000)    
Date of Construction or Acquisition 2003          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 14,532,000          
Deductions during year [Abstract]            
Balance at close of year 5,874,000          
Commercial Healthcare [Member] | Edina 6545 France SMC I - Edina MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       29,622,000    
Initial Cost to Company [Abstract]            
Land       3,480,000    
Buildings & Improvements       30,192,000    
Costs capitalized subsequent to acquisition       14,423,000    
Gross amount at which carried at close of period [Abstract]            
Land       3,480,000    
Buildings & Improvements       44,615,000    
Total 48,095,000     48,095,000    
Accumulated Depreciation $ (17,035,000)     (17,035,000)    
Date of Construction or Acquisition 2001          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 48,095,000          
Deductions during year [Abstract]            
Balance at close of year 17,035,000          
Commercial Healthcare [Member] | Fresenius - Duluth, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       576,000    
Initial Cost to Company [Abstract]            
Land       50,000    
Buildings & Improvements       1,520,000    
Costs capitalized subsequent to acquisition       2,000    
Gross amount at which carried at close of period [Abstract]            
Land       50,000    
Buildings & Improvements       1,522,000    
Total 1,572,000     1,572,000    
Accumulated Depreciation $ (420,000)     (420,000)    
Date of Construction or Acquisition 2004          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,572,000          
Deductions during year [Abstract]            
Balance at close of year 420,000          
Commercial Healthcare [Member] | Garden View - St. Paul, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       0    
Buildings & Improvements       7,408,000    
Costs capitalized subsequent to acquisition       898,000    
Gross amount at which carried at close of period [Abstract]            
Land       26,000    
Buildings & Improvements       8,280,000    
Total 8,306,000     8,306,000    
Accumulated Depreciation $ (2,723,000)     (2,723,000)    
Date of Construction or Acquisition 2002          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 8,306,000          
Deductions during year [Abstract]            
Balance at close of year 2,723,000          
Commercial Healthcare [Member] | Gateway Clinic - Sandstone, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       828,000    
Initial Cost to Company [Abstract]            
Land       66,000    
Buildings & Improvements       1,699,000    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       66,000    
Buildings & Improvements       1,699,000    
Total 1,765,000     1,765,000    
Accumulated Depreciation $ (469,000)     (469,000)    
Date of Construction or Acquisition 2004          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,765,000          
Deductions during year [Abstract]            
Balance at close of year 469,000          
Commercial Healthcare [Member] | Healtheast St John & Woodwinds - Maplewood & Woodbury, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       7,366,000    
Initial Cost to Company [Abstract]            
Land       3,239,000    
Buildings & Improvements       18,362,000    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       3,239,000    
Buildings & Improvements       18,362,000    
Total 21,601,000     21,601,000    
Accumulated Depreciation $ (6,867,000)     (6,867,000)    
Date of Construction or Acquisition 2000          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 21,601,000          
Deductions during year [Abstract]            
Balance at close of year 6,867,000          
Commercial Healthcare [Member] | High Pointe Health Campus - Lake Elmo, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       7,500,000    
Initial Cost to Company [Abstract]            
Land       1,305,000    
Buildings & Improvements       10,528,000    
Costs capitalized subsequent to acquisition       2,091,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,329,000    
Buildings & Improvements       12,595,000    
Total 13,924,000     13,924,000    
Accumulated Depreciation $ (3,750,000)     (3,750,000)    
Date of Construction or Acquisition 2004          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 13,924,000          
Deductions during year [Abstract]            
Balance at close of year 3,750,000          
Commercial Healthcare [Member] | Laramie 1072 N 22nd Street (Spring Wind) - Laramie, WY [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1],[6]       0    
Initial Cost to Company [Abstract]            
Land [6]       406,000    
Buildings & Improvements [6]       10,151,000    
Costs capitalized subsequent to acquisition [6]       27,000    
Gross amount at which carried at close of period [Abstract]            
Land [6]       406,000    
Buildings & Improvements [6]       10,178,000    
Total [6] 10,584,000     10,584,000    
Accumulated Depreciation [6] $ (1,251,000)     (1,251,000)    
Date of Construction or Acquisition [6] 2009          
Life on which depreciation in latest income statement is computed [6] 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year [6] $ 10,584,000          
Deductions during year [Abstract]            
Balance at close of year [6] 1,251,000          
Commercial Healthcare [Member] | Legends at Heritage Place - Sartell, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       970,000    
Buildings & Improvements       9,920,000    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       970,000    
Buildings & Improvements       9,920,000    
Total 10,890,000     10,890,000    
Accumulated Depreciation $ (382,000)     (382,000)    
Date of Construction or Acquisition 2013          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 10,890,000          
Deductions during year [Abstract]            
Balance at close of year 382,000          
Commercial Healthcare [Member] | Mariner Clinic - Superior, WI [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       1,811,000    
Initial Cost to Company [Abstract]            
Land       0    
Buildings & Improvements       3,781,000    
Costs capitalized subsequent to acquisition       90,000    
Gross amount at which carried at close of period [Abstract]            
Land       20,000    
Buildings & Improvements       3,851,000    
Total 3,871,000     3,871,000    
Accumulated Depreciation $ (1,077,000)     (1,077,000)    
Date of Construction or Acquisition 2004          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 3,871,000          
Deductions during year [Abstract]            
Balance at close of year 1,077,000          
Commercial Healthcare [Member] | Minneapolis 701 25th Avenue Medical - Minneapolis, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       7,196,000    
Initial Cost to Company [Abstract]            
Land       0    
Buildings & Improvements       7,873,000    
Costs capitalized subsequent to acquisition       1,566,000    
Gross amount at which carried at close of period [Abstract]            
Land       0    
Buildings & Improvements       9,439,000    
Total 9,439,000     9,439,000    
Accumulated Depreciation $ (1,837,000)     (1,837,000)    
Date of Construction or Acquisition 2008          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 9,439,000          
Deductions during year [Abstract]            
Balance at close of year 1,837,000          
Commercial Healthcare [Member] | Missoula 3050 Great Northern - Missoula, MT [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       1,267,000    
Initial Cost to Company [Abstract]            
Land       640,000    
Buildings & Improvements       1,331,000    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       640,000    
Buildings & Improvements       1,331,000    
Total 1,971,000     1,971,000    
Accumulated Depreciation $ (159,000)     (159,000)    
Date of Construction or Acquisition 2010          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,971,000          
Deductions during year [Abstract]            
Balance at close of year 159,000          
Commercial Healthcare [Member] | Park Dental - Brooklyn Center, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       247,000    
Initial Cost to Company [Abstract]            
Land       185,000    
Buildings & Improvements       2,767,000    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       185,000    
Buildings & Improvements       2,767,000    
Total 2,952,000     2,952,000    
Accumulated Depreciation $ (873,000)     (873,000)    
Date of Construction or Acquisition 2002          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 2,952,000          
Deductions during year [Abstract]            
Balance at close of year 873,000          
Commercial Healthcare [Member] | Pavilion I - Duluth, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       4,773,000    
Initial Cost to Company [Abstract]            
Land       1,245,000    
Buildings & Improvements       8,898,000    
Costs capitalized subsequent to acquisition       31,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,245,000    
Buildings & Improvements       8,929,000    
Total 10,174,000     10,174,000    
Accumulated Depreciation $ (2,445,000)     (2,445,000)    
Date of Construction or Acquisition 2004          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 10,174,000          
Deductions during year [Abstract]            
Balance at close of year 2,445,000          
Commercial Healthcare [Member] | Pavilion II - Duluth, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       8,783,000    
Initial Cost to Company [Abstract]            
Land       2,715,000    
Buildings & Improvements       14,673,000    
Costs capitalized subsequent to acquisition       1,937,000    
Gross amount at which carried at close of period [Abstract]            
Land       2,715,000    
Buildings & Improvements       16,610,000    
Total 19,325,000     19,325,000    
Accumulated Depreciation $ (5,788,000)     (5,788,000)    
Date of Construction or Acquisition 2004          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 19,325,000          
Deductions during year [Abstract]            
Balance at close of year 5,788,000          
Commercial Healthcare [Member] | Ritchie Medical Plaza - St Paul, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       5,980,000    
Initial Cost to Company [Abstract]            
Land       1,615,000    
Buildings & Improvements       7,851,000    
Costs capitalized subsequent to acquisition       3,611,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,647,000    
Buildings & Improvements       11,430,000    
Total 13,077,000     13,077,000    
Accumulated Depreciation $ (2,880,000)     (2,880,000)    
Date of Construction or Acquisition 2005          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 13,077,000          
Deductions during year [Abstract]            
Balance at close of year 2,880,000          
Commercial Healthcare [Member] | Sartell 2000 23rd Street South - Sartell, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       1,593,000    
Initial Cost to Company [Abstract]            
Land       0    
Buildings & Improvements       11,781,000    
Costs capitalized subsequent to acquisition       934,000    
Gross amount at which carried at close of period [Abstract]            
Land       0    
Buildings & Improvements       12,715,000    
Total 12,715,000     12,715,000    
Accumulated Depreciation $ (4,101,000)     (4,101,000)    
Date of Construction or Acquisition 2002          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 12,715,000          
Deductions during year [Abstract]            
Balance at close of year 4,101,000          
Commercial Healthcare [Member] | Spring Creek American Falls- American Falls, ID [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       2,086,000    
Initial Cost to Company [Abstract]            
Land       145,000    
Buildings & Improvements       3,870,000    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       145,000    
Buildings & Improvements       3,870,000    
Total 4,015,000     4,015,000    
Accumulated Depreciation $ (404,000)     (404,000)    
Date of Construction or Acquisition 2011          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 4,015,000          
Deductions during year [Abstract]            
Balance at close of year 404,000          
Commercial Healthcare [Member] | Spring Creek-Boise - Boise, ID [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       2,751,000    
Initial Cost to Company [Abstract]            
Land       708,000    
Buildings & Improvements       4,296,000    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       708,000    
Buildings & Improvements       4,296,000    
Total 5,004,000     5,004,000    
Accumulated Depreciation $ (482,000)     (482,000)    
Date of Construction or Acquisition 2011          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 5,004,000          
Deductions during year [Abstract]            
Balance at close of year 482,000          
Commercial Healthcare [Member] | Spring Creek-Eagle - Eagle, ID [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       1,919,000    
Initial Cost to Company [Abstract]            
Land       263,000    
Buildings & Improvements       3,775,000    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       263,000    
Buildings & Improvements       3,775,000    
Total 4,038,000     4,038,000    
Accumulated Depreciation $ (396,000)     (396,000)    
Date of Construction or Acquisition 2011          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 4,038,000          
Deductions during year [Abstract]            
Balance at close of year 396,000          
Commercial Healthcare [Member] | Spring Creek Fruitland - Fruitland, ID [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       550,000    
Buildings & Improvements       6,565,000    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       550,000    
Buildings & Improvements       6,565,000    
Total 7,115,000     7,115,000    
Accumulated Depreciation $ (260,000)     (260,000)    
Date of Construction or Acquisition 2014          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 7,115,000          
Deductions during year [Abstract]            
Balance at close of year 260,000          
Commercial Healthcare [Member] | Spring Creek-Meridian - Meridian, ID [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       3,171,000    
Initial Cost to Company [Abstract]            
Land       424,000    
Buildings & Improvements       6,724,000    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       424,000    
Buildings & Improvements       6,724,000    
Total 7,148,000     7,148,000    
Accumulated Depreciation $ (698,000)     (698,000)    
Date of Construction or Acquisition 2011          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 7,148,000          
Deductions during year [Abstract]            
Balance at close of year 698,000          
Commercial Healthcare [Member] | Spring Creek-Overland - Overland, ID [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       3,106,000    
Initial Cost to Company [Abstract]            
Land       687,000    
Buildings & Improvements       5,942,000    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       687,000    
Buildings & Improvements       5,942,000    
Total 6,629,000     6,629,000    
Accumulated Depreciation $ (644,000)     (644,000)    
Date of Construction or Acquisition 2011          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 6,629,000          
Deductions during year [Abstract]            
Balance at close of year 644,000          
Commercial Healthcare [Member] | Spring Creek-Soda Springs - Soda Springs, ID [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       751,000    
Initial Cost to Company [Abstract]            
Land       66,000    
Buildings & Improvements       2,124,000    
Costs capitalized subsequent to acquisition       33,000    
Gross amount at which carried at close of period [Abstract]            
Land       66,000    
Buildings & Improvements       2,157,000    
Total 2,223,000     2,223,000    
Accumulated Depreciation $ (228,000)     (228,000)    
Date of Construction or Acquisition 2011          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 2,223,000          
Deductions during year [Abstract]            
Balance at close of year 228,000          
Commercial Healthcare [Member] | Spring Creek-Ustick - Meridian, ID [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       467,000    
Buildings & Improvements       3,833,000    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       467,000    
Buildings & Improvements       3,833,000    
Total 4,300,000     4,300,000    
Accumulated Depreciation $ (370,000)     (370,000)    
Date of Construction or Acquisition 2011          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 4,300,000          
Deductions during year [Abstract]            
Balance at close of year 370,000          
Commercial Healthcare [Member] | St Michael Clinic - St Michael, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       1,795,000    
Initial Cost to Company [Abstract]            
Land       328,000    
Buildings & Improvements       2,259,000    
Costs capitalized subsequent to acquisition       264,000    
Gross amount at which carried at close of period [Abstract]            
Land       328,000    
Buildings & Improvements       2,523,000    
Total 2,851,000     2,851,000    
Accumulated Depreciation $ (510,000)     (510,000)    
Date of Construction or Acquisition 2007          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 2,851,000          
Deductions during year [Abstract]            
Balance at close of year 510,000          
Commercial Healthcare [Member] | Trinity at Plaza 16 - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       4,718,000    
Initial Cost to Company [Abstract]            
Land       568,000    
Buildings & Improvements       9,009,000    
Costs capitalized subsequent to acquisition       125,000    
Gross amount at which carried at close of period [Abstract]            
Land       674,000    
Buildings & Improvements       9,028,000    
Total 9,702,000     9,702,000    
Accumulated Depreciation $ (820,000)     (820,000)    
Date of Construction or Acquisition 2011          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 9,702,000          
Deductions during year [Abstract]            
Balance at close of year 820,000          
Commercial Healthcare [Member] | Wells Clinic - Hibbing, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       1,263,000    
Initial Cost to Company [Abstract]            
Land       162,000    
Buildings & Improvements       2,497,000    
Costs capitalized subsequent to acquisition       2,000    
Gross amount at which carried at close of period [Abstract]            
Land       162,000    
Buildings & Improvements       2,499,000    
Total 2,661,000     2,661,000    
Accumulated Depreciation $ (690,000)     (690,000)    
Date of Construction or Acquisition 2004          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 2,661,000          
Deductions during year [Abstract]            
Balance at close of year 690,000          
Commercial Healthcare [Member] | Wholly Owned Properties [Member]            
Reconciliations of total real estate carrying value [Abstract]            
Additions 0 18,005,000 11,122,000      
Industrial [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       12,404,000    
Initial Cost to Company [Abstract]            
Land       9,040,000    
Buildings & Improvements       43,081,000    
Costs capitalized subsequent to acquisition       8,490,000    
Gross amount at which carried at close of period [Abstract]            
Land       9,336,000    
Buildings & Improvements       51,275,000    
Total 60,611,000     60,611,000    
Accumulated Depreciation (11,256,000)     (11,256,000)    
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year 60,611,000          
Deductions during year [Abstract]            
Balance at close of year 11,256,000          
Industrial [Member] | Bloomington 2000 W 94th Street - Bloomington, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1],[6]       0    
Initial Cost to Company [Abstract]            
Land [6]       2,133,000    
Buildings & Improvements [6]       4,097,000    
Costs capitalized subsequent to acquisition [6]       1,217,000    
Gross amount at which carried at close of period [Abstract]            
Land [6]       2,204,000    
Buildings & Improvements [6]       5,243,000    
Total [6] 7,447,000     7,447,000    
Accumulated Depreciation [6] $ (1,423,000)     (1,423,000)    
Date of Construction or Acquisition [6] 2006          
Life on which depreciation in latest income statement is computed [6] 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year [6] $ 7,447,000          
Deductions during year [Abstract]            
Balance at close of year [6] 1,423,000          
Industrial [Member] | Lexington Commerce Center - Eagan, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       1,604,000    
Initial Cost to Company [Abstract]            
Land       453,000    
Buildings & Improvements       4,352,000    
Costs capitalized subsequent to acquisition       1,977,000    
Gross amount at which carried at close of period [Abstract]            
Land       480,000    
Buildings & Improvements       6,302,000    
Total 6,782,000     6,782,000    
Accumulated Depreciation $ (2,831,000)     (2,831,000)    
Date of Construction or Acquisition 1999          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 6,782,000          
Deductions during year [Abstract]            
Balance at close of year 2,831,000          
Industrial [Member] | Minot IPS - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1],[6]       0    
Initial Cost to Company [Abstract]            
Land [6]       416,000    
Buildings & Improvements [6]       5,952,000    
Costs capitalized subsequent to acquisition [6]       0    
Gross amount at which carried at close of period [Abstract]            
Land [6]       416,000    
Buildings & Improvements [6]       5,952,000    
Total [6] 6,368,000     6,368,000    
Accumulated Depreciation [6] $ (374,000)     (374,000)    
Date of Construction or Acquisition [6] 2012          
Life on which depreciation in latest income statement is computed [6] 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year [6] $ 6,368,000          
Deductions during year [Abstract]            
Balance at close of year [6] 374,000          
Industrial [Member] | Stone Container - Fargo, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       382,000    
Initial Cost to Company [Abstract]            
Land       440,000    
Buildings & Improvements       6,597,000    
Costs capitalized subsequent to acquisition       104,000    
Gross amount at which carried at close of period [Abstract]            
Land       440,000    
Buildings & Improvements       6,701,000    
Total 7,141,000     7,141,000    
Accumulated Depreciation $ (2,943,000)     (2,943,000)    
Date of Construction or Acquisition 2001          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 7,141,000          
Deductions during year [Abstract]            
Balance at close of year 2,943,000          
Industrial [Member] | Roseville 3075 Long Lake Road - Roseville, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       810,000    
Buildings & Improvements       9,562,000    
Costs capitalized subsequent to acquisition       1,326,000    
Gross amount at which carried at close of period [Abstract]            
Land       810,000    
Buildings & Improvements       10,888,000    
Total 11,698,000     11,698,000    
Accumulated Depreciation $ (145,000)     (145,000)    
Date of Construction or Acquisition 2001          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 11,698,000          
Deductions during year [Abstract]            
Balance at close of year 145,000          
Industrial [Member] | Urbandale 3900 106th Street - Urbandale, IA [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       10,418,000    
Initial Cost to Company [Abstract]            
Land       3,680,000    
Buildings & Improvements       9,893,000    
Costs capitalized subsequent to acquisition       1,982,000    
Gross amount at which carried at close of period [Abstract]            
Land       3,863,000    
Buildings & Improvements       11,692,000    
Total 15,555,000     15,555,000    
Accumulated Depreciation $ (2,553,000)     (2,553,000)    
Date of Construction or Acquisition 2007          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 15,555,000          
Deductions during year [Abstract]            
Balance at close of year 2,553,000          
Industrial [Member] | Woodbury 1865 Woodlane - Woodbury, MN [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       0    
Initial Cost to Company [Abstract]            
Land       1,108,000    
Buildings & Improvements       2,628,000    
Costs capitalized subsequent to acquisition       1,884,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,123,000    
Buildings & Improvements       4,497,000    
Total 5,620,000     5,620,000    
Accumulated Depreciation $ (987,000)     (987,000)    
Date of Construction or Acquisition 2007          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 5,620,000          
Deductions during year [Abstract]            
Balance at close of year 987,000          
Industrial [Member] | Wholly Owned Properties [Member]            
Reconciliations of total real estate carrying value [Abstract]            
Additions 9,037,000 0 5,900,000      
Other Property [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       11,685,000    
Initial Cost to Company [Abstract]            
Land       3,640,000    
Buildings & Improvements       24,933,000    
Costs capitalized subsequent to acquisition       15,642,000    
Gross amount at which carried at close of period [Abstract]            
Land       4,057,000    
Buildings & Improvements       40,158,000    
Total 44,215,000     44,215,000    
Accumulated Depreciation (9,123,000)     (9,123,000)    
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year 44,215,000          
Deductions during year [Abstract]            
Balance at close of year 9,123,000          
Other Property [Member] | 1st Avenue Building - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       0    
Initial Cost to Company [Abstract]            
Land       30,000    
Buildings & Improvements       337,000    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       30,000    
Buildings & Improvements       337,000    
Total 367,000     367,000    
Accumulated Depreciation $ (41,000)     (41,000)    
Date of Construction or Acquisition 1981          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 367,000          
Deductions during year [Abstract]            
Balance at close of year $ 41,000          
Other Property [Member] | 1st Avenue Building - Minot, ND [Member] | Minimum [Member]            
Gross amount at which carried at close of period [Abstract]            
Life on which depreciation in latest income statement is computed 33 years          
Other Property [Member] | 1st Avenue Building - Minot, ND [Member] | Maximum [Member]            
Gross amount at which carried at close of period [Abstract]            
Life on which depreciation in latest income statement is computed 40 years          
Other Property [Member] | Bismarck 715 East Broadway - Bismarck, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       2,103,000    
Initial Cost to Company [Abstract]            
Land       389,000    
Buildings & Improvements       1,283,000    
Costs capitalized subsequent to acquisition       1,126,000    
Gross amount at which carried at close of period [Abstract]            
Land       443,000    
Buildings & Improvements       2,355,000    
Total $ 2,798,000     2,798,000    
Accumulated Depreciation $ (458,000)     (458,000)    
Date of Construction or Acquisition 2008          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 2,798,000          
Deductions during year [Abstract]            
Balance at close of year 458,000          
Other Property [Member] | Minot 1400 31st Ave - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       0    
Initial Cost to Company [Abstract]            
Land       1,026,000    
Buildings & Improvements       6,143,000    
Costs capitalized subsequent to acquisition       4,404,000    
Gross amount at which carried at close of period [Abstract]            
Land       1,038,000    
Buildings & Improvements       10,535,000    
Total 11,573,000     11,573,000    
Accumulated Depreciation $ (2,287,000)     (2,287,000)    
Date of Construction or Acquisition 2010          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 11,573,000          
Deductions during year [Abstract]            
Balance at close of year 2,287,000          
Other Property [Member] | Minot 2505 16th Street SW - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       0    
Initial Cost to Company [Abstract]            
Land       298,000    
Buildings & Improvements       1,724,000    
Costs capitalized subsequent to acquisition       296,000    
Gross amount at which carried at close of period [Abstract]            
Land       298,000    
Buildings & Improvements       2,020,000    
Total 2,318,000     2,318,000    
Accumulated Depreciation $ (275,000)     (275,000)    
Date of Construction or Acquisition 2009          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 2,318,000          
Deductions during year [Abstract]            
Balance at close of year 275,000          
Other Property [Member] | Plaza 16 - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       7,098,000    
Initial Cost to Company [Abstract]            
Land       389,000    
Buildings & Improvements       5,444,000    
Costs capitalized subsequent to acquisition       3,859,000    
Gross amount at which carried at close of period [Abstract]            
Land       598,000    
Buildings & Improvements       9,094,000    
Total 9,692,000     9,692,000    
Accumulated Depreciation $ (2,041,000)     (2,041,000)    
Date of Construction or Acquisition 2009          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 9,692,000          
Deductions during year [Abstract]            
Balance at close of year 2,041,000          
Other Property [Member] | 17 South Main - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       75,000    
Initial Cost to Company [Abstract]            
Land       15,000    
Buildings & Improvements       75,000    
Costs capitalized subsequent to acquisition       197,000    
Gross amount at which carried at close of period [Abstract]            
Land       17,000    
Buildings & Improvements       270,000    
Total 287,000     287,000    
Accumulated Depreciation $ (202,000)     (202,000)    
Date of Construction or Acquisition 2000          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 287,000          
Deductions during year [Abstract]            
Balance at close of year 202,000          
Other Property [Member] | Arrowhead First International Bank - Minot ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       0    
Initial Cost to Company [Abstract]            
Land       75,000    
Buildings & Improvements       1,211,000    
Costs capitalized subsequent to acquisition       20,000    
Gross amount at which carried at close of period [Abstract]            
Land       95,000    
Buildings & Improvements       1,211,000    
Total 1,306,000     1,306,000    
Accumulated Depreciation $ (65,000)     (65,000)    
Date of Construction or Acquisition 2013          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 1,306,000          
Deductions during year [Abstract]            
Balance at close of year 65,000          
Other Property [Member] | Dakota West Plaza - Minot , ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       347,000    
Initial Cost to Company [Abstract]            
Land       92,000    
Buildings & Improvements       493,000    
Costs capitalized subsequent to acquisition       30,000    
Gross amount at which carried at close of period [Abstract]            
Land       106,000    
Buildings & Improvements       509,000    
Total 615,000     615,000    
Accumulated Depreciation $ (122,000)     (122,000)    
Date of Construction or Acquisition 2006          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 615,000          
Deductions during year [Abstract]            
Balance at close of year 122,000          
Other Property [Member] | Grand Forks Carmike - Grand Forks, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       1,304,000    
Initial Cost to Company [Abstract]            
Land       184,000    
Buildings & Improvements       2,360,000    
Costs capitalized subsequent to acquisition       2,000    
Gross amount at which carried at close of period [Abstract]            
Land       184,000    
Buildings & Improvements       2,362,000    
Total 2,546,000     2,546,000    
Accumulated Depreciation $ (1,211,000)     (1,211,000)    
Date of Construction or Acquisition 1994          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 2,546,000          
Deductions during year [Abstract]            
Balance at close of year 1,211,000          
Other Property [Member] | Minot Arrowhead - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       0    
Initial Cost to Company [Abstract]            
Land       100,000    
Buildings & Improvements       3,216,000    
Costs capitalized subsequent to acquisition       5,553,000    
Gross amount at which carried at close of period [Abstract]            
Land       176,000    
Buildings & Improvements       8,693,000    
Total 8,869,000     8,869,000    
Accumulated Depreciation $ (2,058,000)     (2,058,000)    
Date of Construction or Acquisition 1973          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 8,869,000          
Deductions during year [Abstract]            
Balance at close of year 2,058,000          
Other Property [Member] | Minot Plaza - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       758,000    
Initial Cost to Company [Abstract]            
Land       50,000    
Buildings & Improvements       453,000    
Costs capitalized subsequent to acquisition       155,000    
Gross amount at which carried at close of period [Abstract]            
Land       80,000    
Buildings & Improvements       578,000    
Total 658,000     658,000    
Accumulated Depreciation $ (339,000)     (339,000)    
Date of Construction or Acquisition 1993          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 658,000          
Deductions during year [Abstract]            
Balance at close of year 339,000          
Other Property [Member] | Minot Southgate Wells Fargo Bank - Minot, ND [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances       0    
Initial Cost to Company [Abstract]            
Land       992,000    
Buildings & Improvements       2,194,000    
Costs capitalized subsequent to acquisition       0    
Gross amount at which carried at close of period [Abstract]            
Land       992,000    
Buildings & Improvements       2,194,000    
Total 3,186,000     3,186,000    
Accumulated Depreciation $ (24,000)     (24,000)    
Date of Construction or Acquisition 2014          
Life on which depreciation in latest income statement is computed 40 years          
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year $ 3,186,000          
Deductions during year [Abstract]            
Balance at close of year 24,000          
Other Property [Member] | Wholly Owned Properties [Member]            
Reconciliations of total real estate carrying value [Abstract]            
Additions 3,186,000 $ 0 $ 1,240,000      
Subtotal [Member]            
Real Estate And Accumulated Depreciation [Abstract]            
Encumbrances [1]       667,544,000    
Initial Cost to Company [Abstract]            
Land       111,612,000    
Buildings & Improvements       1,223,659,000    
Costs capitalized subsequent to acquisition       211,096,000    
Gross amount at which carried at close of period [Abstract]            
Land       129,513,000    
Buildings & Improvements       1,416,854,000    
Total 1,546,367,000     1,546,367,000    
Accumulated Depreciation (313,308,000)     $ (313,308,000)    
Reconciliations of total real estate carrying value [Abstract]            
Balance at close of year 1,546,367,000          
Deductions during year [Abstract]            
Balance at close of year $ 313,308,000          
[1] Amounts in this column are the mortgages payable balances as of April 30, 2015. These amounts do not include amounts owing under the Company's multi-bank line of credit or under the Company's construction loans.
[2] The net basis of the Company's real estate investments for Federal Income Tax purposes was $1.7 billion, $1.5 billion and $1.5 billion at April 30, 2015, 2014 and 2013, respectively.
[3] Consists of miscellaneous disposed assets.
[4] Includes development projects that are placed in service in phases.
[5] Consists of miscellaneous re-classed assets.
[6] As of April 30, 2015, this property was included in the collateral pool securing the Company's $90.0 million multi-bank line of credit. The Company may add and remove eligible properties from the collateral pool if certain minimum collateral requirements are satisfied. Advances under the facility may not exceed 60% of the value of properties provided as security.