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Schedule III - Real Estate and Accumulated Depreciation (Details)
 12 Months Ended
Dec. 31, 2020
USD ($)
ApartmentUnit
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Real Estate And Accumulated Depreciation Abstract        
Accumulated Depreciation $ (7,859,657,000) $ (7,276,786,000) $ (6,696,281,000) $ (6,040,378,000)
100 K Apartments (fka 100K Street) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 222      
Initial Cost to Company, Land $ 15,600,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 70,296,069      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 18,484      
Gross Amount Carried at close of period 12/31/2020, Land 15,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 70,314,553      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 85,914,553      
Accumulated Depreciation (6,076,767)      
Investment in Real Estate, Net 79,837,786      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
140 Riverside Boulevard [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 354      
Initial Cost to Company, Land $ 103,539,100      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 94,082,725      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 10,817,358      
Gross Amount Carried at close of period 12/31/2020, Land 103,539,100      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 104,900,083      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 208,439,183      
Accumulated Depreciation (56,324,733)      
Investment in Real Estate, Net 152,114,450      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
160 Riverside Boulevard [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 455      
Initial Cost to Company, Land $ 139,933,500      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 190,964,745      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 18,135,193      
Gross Amount Carried at close of period 12/31/2020, Land 139,933,500      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 209,099,938      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 349,033,438      
Accumulated Depreciation (112,149,211)      
Investment in Real Estate, Net 236,884,227      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
170 Amsterdam [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 236      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 112,096,955      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 734,040      
Gross Amount Carried at close of period 12/31/2020, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 112,830,995      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 112,830,995      
Accumulated Depreciation (25,078,672)      
Investment in Real Estate, Net 87,752,323      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
175 Kent [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Brooklyn, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 113      
Initial Cost to Company, Land $ 22,037,831      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 53,962,169      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,476,612      
Gross Amount Carried at close of period 12/31/2020, Land 22,037,831      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 56,438,781      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 78,476,612      
Accumulated Depreciation (20,147,633)      
Investment in Real Estate, Net 58,328,979      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
180 Montague (fka Brooklyn Heights) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Brooklyn, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 193      
Initial Cost to Company, Land $ 32,400,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 92,675,228      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,346,485      
Gross Amount Carried at close of period 12/31/2020, Land 32,400,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 98,021,713      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 130,421,713      
Accumulated Depreciation (30,697,551)      
Investment in Real Estate, Net 99,724,162      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
180 Riverside Boulevard [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 516      
Initial Cost to Company, Land $ 144,968,250      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 138,346,681      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 16,593,445      
Gross Amount Carried at close of period 12/31/2020, Land 144,968,250      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 154,940,126      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 299,908,376      
Accumulated Depreciation (83,930,689)      
Investment in Real Estate, Net 215,977,687      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
1210 Mass [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 144      
Initial Cost to Company, Land $ 9,213,512      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 36,559,189      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,222,293      
Gross Amount Carried at close of period 12/31/2020, Land 9,213,512      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 39,781,482      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 48,994,994      
Accumulated Depreciation (21,574,097)      
Investment in Real Estate, Net 27,420,897      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
1401 Joyce on Pentagon Row [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 326      
Initial Cost to Company, Land $ 9,780,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 89,668,165      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,636,363      
Gross Amount Carried at close of period 12/31/2020, Land 9,780,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 95,304,528      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 105,084,528      
Accumulated Depreciation (41,418,326)      
Investment in Real Estate, Net 63,666,202      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
1500 Mass Ave [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 556      
Initial Cost to Company, Land $ 54,638,298      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 40,361,702      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 16,685,633      
Gross Amount Carried at close of period 12/31/2020, Land 54,638,298      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 57,047,335      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 111,685,633      
Accumulated Depreciation (31,601,970)      
Investment in Real Estate, Net 80,083,663      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
1800 Oak (fka Rosslyn) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 314      
Initial Cost to Company, Land $ 31,400,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 109,005,734      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 8,912,514      
Gross Amount Carried at close of period 12/31/2020, Land 31,400,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 117,918,248      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 149,318,248      
Accumulated Depreciation (37,308,243)      
Investment in Real Estate, Net 112,010,005      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
2201 Pershing Drive [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 188      
Initial Cost to Company, Land $ 11,321,198      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 49,674,175      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,798,189      
Gross Amount Carried at close of period 12/31/2020, Land 11,321,198      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 52,472,364      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 63,793,562      
Accumulated Depreciation (17,223,799)      
Investment in Real Estate, Net 46,569,763      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
2201 Wilson [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 219      
Initial Cost to Company, Land $ 21,900,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 78,724,663      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,288,939      
Gross Amount Carried at close of period 12/31/2020, Land 21,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 84,013,602      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 105,913,602      
Accumulated Depreciation (26,463,239)      
Investment in Real Estate, Net 79,450,363      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
2400 M St [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 359      
Initial Cost to Company, Land $ 30,006,593      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 114,013,785      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,779,484      
Gross Amount Carried at close of period 12/31/2020, Land 30,006,593      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 118,793,269      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 148,799,862      
Accumulated Depreciation (61,688,804)      
Investment in Real Estate, Net 87,111,058      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
315 on A [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Boston, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 202      
Initial Cost to Company, Land $ 14,450,070      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 115,824,930      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,442,998      
Gross Amount Carried at close of period 12/31/2020, Land 14,450,070      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 117,267,928      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 131,717,998      
Accumulated Depreciation (27,148,732)      
Investment in Real Estate, Net 104,569,266      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
340 Fremont (fka Rincon Hill) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Francisco, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 348      
Initial Cost to Company, Land $ 42,000,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 248,608,702      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 366,576      
Gross Amount Carried at close of period 12/31/2020, Land 42,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 248,975,278      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 290,975,278      
Accumulated Depreciation (43,051,114)      
Investment in Real Estate, Net 247,924,164      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
341 Nevins [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Brooklyn, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 3,621,717      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 261,079      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2020, Land 3,621,717      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 261,079      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 3,882,796      
Accumulated Depreciation 0      
Investment in Real Estate, Net 3,882,796      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
3003 Van Ness (fka Van Ness) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 625      
Initial Cost to Company, Land $ 56,300,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 141,191,580      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 8,427,901      
Gross Amount Carried at close of period 12/31/2020, Land 56,300,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 149,619,481      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 205,919,481      
Accumulated Depreciation (49,200,506)      
Investment in Real Estate, Net 156,718,975      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
425 Mass [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 559      
Initial Cost to Company, Land $ 28,150,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 138,600,000      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,317,169      
Gross Amount Carried at close of period 12/31/2020, Land 28,150,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 143,917,169      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 172,067,169      
Accumulated Depreciation (58,212,092)      
Investment in Real Estate, Net 113,855,077      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
455 Eye Street [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 174      
Initial Cost to Company, Land $ 11,941,407      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 61,418,689      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 59,540      
Gross Amount Carried at close of period 12/31/2020, Land 11,941,407      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 61,478,229      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 73,419,636      
Accumulated Depreciation (8,480,027)      
Investment in Real Estate, Net 64,939,609      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
4th and Hill [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 13,131,456      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 18,548,300      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2020, Land 13,131,456      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 18,548,300      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 31,679,756      
Accumulated Depreciation 0      
Investment in Real Estate, Net 31,679,756      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
55 West Fifth I & II (fka Townhouse Plaza and Gardens) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Mateo, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 241      
Initial Cost to Company, Land $ 21,041,710      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 71,931,323      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 14,359,593      
Gross Amount Carried at close of period 12/31/2020, Land 21,041,710      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 86,290,916      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 107,332,626      
Accumulated Depreciation (32,617,071)      
Investment in Real Estate, Net 74,715,555      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
600 Washington [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 135      
Initial Cost to Company, Land $ 32,852,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 43,140,551      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,440,539      
Gross Amount Carried at close of period 12/31/2020, Land 32,852,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 45,581,090      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 78,433,090      
Accumulated Depreciation (23,873,446)      
Investment in Real Estate, Net 54,559,644      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
660 Washington (fka Boston Common) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Boston, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 420      
Initial Cost to Company, Land $ 106,100,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 166,311,679      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,631,972      
Gross Amount Carried at close of period 12/31/2020, Land 106,100,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 173,943,651      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 280,043,651      
Accumulated Depreciation (52,935,820)      
Investment in Real Estate, Net 227,107,831      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
70 Greene [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Jersey City, NJ      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 480      
Initial Cost to Company, Land $ 28,108,899      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 236,763,553      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,894,770      
Gross Amount Carried at close of period 12/31/2020, Land 28,108,899      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 240,658,323      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 268,767,222      
Accumulated Depreciation (90,074,628)      
Investment in Real Estate, Net 178,692,594      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
71 Broadway [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 238      
Initial Cost to Company, Land $ 22,611,600      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 77,492,171      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 18,570,618      
Gross Amount Carried at close of period 12/31/2020, Land 22,611,600      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 96,062,789      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 118,674,389      
Accumulated Depreciation (55,283,708)      
Investment in Real Estate, Net 63,390,681      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
77 Bluxome [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Francisco, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 102      
Initial Cost to Company, Land $ 5,249,124      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 18,609,876      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 498,937      
Gross Amount Carried at close of period 12/31/2020, Land 5,249,124      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 19,108,813      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 24,357,937      
Accumulated Depreciation (7,020,181)      
Investment in Real Estate, Net 17,337,756      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
77 Park Avenue (fka Hoboken) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Hoboken, NJ      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 301      
Initial Cost to Company, Land $ 27,900,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 168,992,440      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 8,837,952      
Gross Amount Carried at close of period 12/31/2020, Land 27,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 177,830,392      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 205,730,392      
Accumulated Depreciation (54,327,929)      
Investment in Real Estate, Net 151,402,463      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
777 Sixth [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 294      
Initial Cost to Company, Land $ 65,352,706      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 65,747,294      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,748,406      
Gross Amount Carried at close of period 12/31/2020, Land 65,352,706      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 71,495,700      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 136,848,406      
Accumulated Depreciation (33,061,181)      
Investment in Real Estate, Net 103,787,225      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
88 Hillside [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Daly City, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 95      
Initial Cost to Company, Land $ 7,786,800      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 31,587,325      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,442,015      
Gross Amount Carried at close of period 12/31/2020, Land 7,786,800      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 35,029,340      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 42,816,140      
Accumulated Depreciation (12,829,331)      
Investment in Real Estate, Net 29,986,809      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
855 Brannan [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Francisco, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 449      
Initial Cost to Company, Land $ 41,363,921      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 282,133,994      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 132,534      
Gross Amount Carried at close of period 12/31/2020, Land 41,363,921      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 282,266,528      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 323,630,449      
Accumulated Depreciation (34,706,782)      
Investment in Real Estate, Net 288,923,667      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
929 Mass (fka 929 House) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Cambridge, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 127      
Initial Cost to Company, Land $ 3,252,993      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 21,745,595      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 8,432,225      
Gross Amount Carried at close of period 12/31/2020, Land 3,252,993      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 30,177,820      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 33,430,813      
Accumulated Depreciation (21,091,399)      
Investment in Real Estate, Net 12,339,414      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Academy Village [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location North Hollywood, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 248      
Initial Cost to Company, Land $ 25,000,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 23,593,194      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 11,156,576      
Gross Amount Carried at close of period 12/31/2020, Land 25,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 34,749,770      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 59,749,770      
Accumulated Depreciation (21,580,086)      
Investment in Real Estate, Net 38,169,684      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Acappella [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Pasadena, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 143      
Initial Cost to Company, Land $ 5,839,548      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 29,360,452      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,419,827      
Gross Amount Carried at close of period 12/31/2020, Land 5,839,548      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 31,780,279      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 37,619,827      
Accumulated Depreciation (13,423,512)      
Investment in Real Estate, Net 24,196,315      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Acton Courtyard [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Berkeley, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 71      
Initial Cost to Company, Land $ 5,550,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 15,785,509      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 445,554      
Gross Amount Carried at close of period 12/31/2020, Land 5,550,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 16,231,063      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 21,781,063      
Accumulated Depreciation (8,147,133)      
Investment in Real Estate, Net 13,633,930      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Alban Towers [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 229      
Initial Cost to Company, Land $ 18,900,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 89,794,201      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,195,879      
Gross Amount Carried at close of period 12/31/2020, Land 18,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 96,990,080      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 115,890,080      
Accumulated Depreciation (29,449,847)      
Investment in Real Estate, Net 86,440,233      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Alborada [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Fremont, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 442      
Initial Cost to Company, Land $ 24,310,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 59,214,129      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 9,737,294      
Gross Amount Carried at close of period 12/31/2020, Land 24,310,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 68,951,423      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 93,261,423      
Accumulated Depreciation (47,184,982)      
Investment in Real Estate, Net 46,076,441      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Alcott Apartments (fka West End Tower) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Boston, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 10,424,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 257,358,529      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2020, Land 10,424,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 257,358,529      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 267,782,529      
Accumulated Depreciation 0      
Investment in Real Estate, Net 267,782,529      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Altitude (fka Village at Howard Hughes, The (Lots 1 & 2)) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 545      
Initial Cost to Company, Land $ 43,783,485      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 150,235,105      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 612,403      
Gross Amount Carried at close of period 12/31/2020, Land 43,783,485      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 150,847,508      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 194,630,993      
Accumulated Depreciation (26,754,900)      
Investment in Real Estate, Net 167,876,093      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Alton, The (fka Millikan) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Irvine, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 344      
Initial Cost to Company, Land $ 11,049,027      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 96,524,128      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 243,844      
Gross Amount Carried at close of period 12/31/2020, Land 11,049,027      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 96,767,972      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 107,816,999      
Accumulated Depreciation (15,320,884)      
Investment in Real Estate, Net 92,496,115      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Arbor Terrace [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Sunnyvale, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 175      
Initial Cost to Company, Land $ 9,057,300      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 18,483,642      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 11,966,964      
Gross Amount Carried at close of period 12/31/2020, Land 9,057,300      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 30,450,606      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 39,507,906      
Accumulated Depreciation (19,584,926)      
Investment in Real Estate, Net 19,922,980      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Arches,The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Sunnyvale, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 410      
Initial Cost to Company, Land $ 26,650,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 62,850,000      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,279,238      
Gross Amount Carried at close of period 12/31/2020, Land 26,650,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 66,129,238      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 92,779,238      
Accumulated Depreciation (27,016,180)      
Investment in Real Estate, Net 65,763,058      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Artisan on Second [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 118      
Initial Cost to Company, Land $ 8,000,400      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 36,074,600      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,298,143      
Gross Amount Carried at close of period 12/31/2020, Land 8,000,400      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 37,372,743      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 45,373,143      
Accumulated Depreciation (14,173,055)      
Investment in Real Estate, Net 31,200,088      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Artistry Emeryville (fka Emeryville) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Emeryville, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 267      
Initial Cost to Company, Land $ 12,300,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 61,466,267      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,368,364      
Gross Amount Carried at close of period 12/31/2020, Land 12,300,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 68,834,631      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 81,134,631      
Accumulated Depreciation (23,980,609)      
Investment in Real Estate, Net 57,154,022      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Atelier [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Brooklyn, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 120      
Initial Cost to Company, Land $ 32,401,680      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 47,135,432      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 515,334      
Gross Amount Carried at close of period 12/31/2020, Land 32,401,680      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 47,650,766      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 80,052,446      
Accumulated Depreciation (10,219,483)      
Investment in Real Estate, Net 69,832,963      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Avenue Two [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Redwood City, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 123      
Initial Cost to Company, Land $ 7,995,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 18,005,000      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,509,228      
Gross Amount Carried at close of period 12/31/2020, Land 7,995,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 20,514,228      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 28,509,228      
Accumulated Depreciation (8,409,710)      
Investment in Real Estate, Net 20,099,518      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Axis at Shady Grove [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Rockville, MD      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 366      
Initial Cost to Company, Land $ 14,745,774      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 90,503,831      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 240,588      
Gross Amount Carried at close of period 12/31/2020, Land 14,745,774      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 90,744,419      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 105,490,193      
Accumulated Depreciation (11,084,271)      
Investment in Real Estate, Net 94,405,922      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Azure (fka Mission Bay-Block 13) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Francisco, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 273      
Initial Cost to Company, Land $ 32,855,115      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 153,567,641      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 479,066      
Gross Amount Carried at close of period 12/31/2020, Land 32,855,115      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 154,046,707      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 186,901,822      
Accumulated Depreciation (30,930,604)      
Investment in Real Estate, Net 155,971,218      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Bay Hill [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Long Beach, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 160      
Initial Cost to Company, Land $ 7,600,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 27,437,239      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,043,249      
Gross Amount Carried at close of period 12/31/2020, Land 7,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 31,480,488      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 39,080,488      
Accumulated Depreciation (17,947,925)      
Investment in Real Estate, Net 21,132,563      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Beatrice, The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 302      
Initial Cost to Company, Land $ 114,351,405      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 165,648,595      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,437,470      
Gross Amount Carried at close of period 12/31/2020, Land 114,351,405      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 168,086,065      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 282,437,470      
Accumulated Depreciation (56,957,402)      
Investment in Real Estate, Net 225,480,068      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Bella Vista I, II, III Combined [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Woodland Hills, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 579      
Initial Cost to Company, Land $ 31,682,754      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 121,095,786      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 11,255,581      
Gross Amount Carried at close of period 12/31/2020, Land 31,682,754      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 132,351,367      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 164,034,121      
Accumulated Depreciation (68,433,638)      
Investment in Real Estate, Net 95,600,483      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Belle Arts Condominium Homes, LLC [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Bellevue, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 1      
Initial Cost to Company, Land $ 63,158      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 236,157      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,098      
Gross Amount Carried at close of period 12/31/2020, Land 63,158      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 238,255      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 301,413      
Accumulated Depreciation (99,931)      
Investment in Real Estate, Net 201,482      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Bella Fontaine [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Marina Del Rey, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 102      
Initial Cost to Company, Land $ 9,098,808      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 28,701,192      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,356,766      
Gross Amount Carried at close of period 12/31/2020, Land 9,098,808      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 31,057,958      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 40,156,766      
Accumulated Depreciation (11,041,933)      
Investment in Real Estate, Net 29,114,833      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Breakwater at Marina Del Rey [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Marina Del Rey, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 224      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 73,189,262      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,420,327      
Gross Amount Carried at close of period 12/31/2020, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 75,609,589      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 75,609,589      
Accumulated Depreciation (25,201,234)      
Investment in Real Estate, Net 50,408,355      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Briarwood (CA) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Sunnyvale, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 192      
Initial Cost to Company, Land $ 9,991,500      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 22,247,278      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,418,254      
Gross Amount Carried at close of period 12/31/2020, Land 9,991,500      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 26,665,532      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 36,657,032      
Accumulated Depreciation (20,063,847)      
Investment in Real Estate, Net 16,593,185      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Brodie, The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Westminster, CO      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 312      
Initial Cost to Company, Land $ 8,639,904      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 79,254,618      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 685,818      
Gross Amount Carried at close of period 12/31/2020, Land 8,639,904      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 79,940,436      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 88,580,340      
Accumulated Depreciation (8,800,355)      
Investment in Real Estate, Net 79,779,985      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Brooklyner (fka 111 Lawrence) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Brooklyn, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 490      
Initial Cost to Company, Land $ 40,099,922      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 221,438,631      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,139,174      
Gross Amount Carried at close of period 12/31/2020, Land 40,099,922      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 226,577,805      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 266,677,727      
Accumulated Depreciation (77,766,873)      
Investment in Real Estate, Net 188,910,854      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
C on Pico [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 94      
Initial Cost to Company, Land $ 17,125,766      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 28,074,234      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 607,130      
Gross Amount Carried at close of period 12/31/2020, Land 17,125,766      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 28,681,364      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 45,807,130      
Accumulated Depreciation (6,042,014)      
Investment in Real Estate, Net 39,765,116      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Carlyle Mill [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Alexandria, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 317      
Initial Cost to Company, Land $ 10,000,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 51,367,913      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 9,482,880      
Gross Amount Carried at close of period 12/31/2020, Land 10,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 60,850,793      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 70,850,793      
Accumulated Depreciation (37,283,170)      
Investment in Real Estate, Net 33,567,623      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Carmel Terrace [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Diego, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 384      
Initial Cost to Company, Land $ 2,288,300      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 20,596,281      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 12,821,204      
Gross Amount Carried at close of period 12/31/2020, Land 2,288,300      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 33,417,485      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 35,705,785      
Accumulated Depreciation (29,568,634)      
Investment in Real Estate, Net 6,137,151      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Cascade [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 477      
Initial Cost to Company, Land $ 23,751,564      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 149,384,842      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 58,556      
Gross Amount Carried at close of period 12/31/2020, Land 23,751,564      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 149,443,398      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 173,194,962      
Accumulated Depreciation (20,377,508)      
Investment in Real Estate, Net 152,817,454      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Centennial (fka Centennial Court & Centennial Tower) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 408      
Initial Cost to Company, Land $ 9,700,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 70,080,378      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 14,204,709      
Gross Amount Carried at close of period 12/31/2020, Land 9,700,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 84,285,087      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 93,985,087      
Accumulated Depreciation (47,446,620)      
Investment in Real Estate, Net 46,538,467      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Centre Club Combined [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Ontario, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 412      
Initial Cost to Company, Land $ 7,436,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 33,014,789      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 9,778,429      
Gross Amount Carried at close of period 12/31/2020, Land 7,436,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 42,793,218      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 50,229,218      
Accumulated Depreciation (28,483,810)      
Investment in Real Estate, Net 21,745,408      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Chelsea Square [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Redmond, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 113      
Initial Cost to Company, Land $ 3,397,100      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 9,289,074      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,046,308      
Gross Amount Carried at close of period 12/31/2020, Land 3,397,100      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 12,335,382      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 15,732,482      
Accumulated Depreciation (9,272,305)      
Investment in Real Estate, Net 6,460,177      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Chloe on Madison (fka 1401 E. Madison) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 137      
Initial Cost to Company, Land $ 10,401,958      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 53,750,777      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,916      
Gross Amount Carried at close of period 12/31/2020, Land 10,401,958      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 53,753,693      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 64,155,651      
Accumulated Depreciation (2,655,541)      
Investment in Real Estate, Net 61,500,110      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Chloe on Union (fka Chloe) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 117      
Initial Cost to Company, Land $ 14,835,571      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 39,359,650      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,872,330      
Gross Amount Carried at close of period 12/31/2020, Land 14,835,571      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 42,231,980      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 57,067,551      
Accumulated Depreciation (6,417,475)      
Investment in Real Estate, Net 50,650,076      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Church Corner [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Cambridge, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 85      
Initial Cost to Company, Land $ 5,220,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 16,744,643      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,414,899      
Gross Amount Carried at close of period 12/31/2020, Land 5,220,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 20,159,542      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 25,379,542      
Accumulated Depreciation (11,781,658)      
Investment in Real Estate, Net 13,597,884      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
City Gate at Cupertino (fka Cupertino) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Cupertino, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 311      
Initial Cost to Company, Land $ 40,400,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 95,937,046      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,718,239      
Gross Amount Carried at close of period 12/31/2020, Land 40,400,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 103,655,285      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 144,055,285      
Accumulated Depreciation (33,293,690)      
Investment in Real Estate, Net 110,761,595      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
City Square Bellevue (fka Bellevue) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Bellevue, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 191      
Initial Cost to Company, Land $ 15,100,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 41,876,257      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,956,888      
Gross Amount Carried at close of period 12/31/2020, Land 15,100,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 45,833,145      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 60,933,145      
Accumulated Depreciation (15,186,445)      
Investment in Real Estate, Net 45,746,700      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Clarendon, The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 292      
Initial Cost to Company, Land $ 30,400,340      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 103,824,660      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,799,573      
Gross Amount Carried at close of period 12/31/2020, Land 30,400,340      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 106,624,233      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 137,024,573      
Accumulated Depreciation (40,439,940)      
Investment in Real Estate, Net 96,584,633      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Cleo, The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 92      
Initial Cost to Company, Land $ 6,615,467      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 14,829,335      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,278,181      
Gross Amount Carried at close of period 12/31/2020, Land 6,615,467      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 19,107,516      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 25,722,983      
Accumulated Depreciation (10,359,000)      
Investment in Real Estate, Net 15,363,983      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Connecticut Heights [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 518      
Initial Cost to Company, Land $ 27,600,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 114,002,295      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 10,672,491      
Gross Amount Carried at close of period 12/31/2020, Land 27,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 124,674,786      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 152,274,786      
Accumulated Depreciation (38,864,851)      
Investment in Real Estate, Net 113,409,935      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Corcoran House at DuPont Circle (fka DuPont Circle) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 138      
Initial Cost to Company, Land $ 13,500,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 26,913,113      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,106,014      
Gross Amount Carried at close of period 12/31/2020, Land 13,500,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 31,019,127      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 44,519,127      
Accumulated Depreciation (10,154,028)      
Investment in Real Estate, Net 34,365,099      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Courthouse Plaza [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 396      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 87,386,024      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,926,335      
Gross Amount Carried at close of period 12/31/2020, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 94,312,359      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 94,312,359      
Accumulated Depreciation (31,836,593)      
Investment in Real Estate, Net 62,475,766      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Creekside (San Mateo) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Mateo, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 192      
Initial Cost to Company, Land $ 9,606,600      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 21,193,232      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,528,464      
Gross Amount Carried at close of period 12/31/2020, Land 9,606,600      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 26,721,696      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 36,328,296      
Accumulated Depreciation (19,983,009)      
Investment in Real Estate, Net 16,345,287      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Cronins Landing [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Waltham, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 281      
Initial Cost to Company, Land $ 32,300,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 85,119,324      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 12,705,880      
Gross Amount Carried at close of period 12/31/2020, Land 32,300,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 97,825,204      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 130,125,204      
Accumulated Depreciation (31,367,886)      
Investment in Real Estate, Net 98,757,318      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Crystal Place [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 181      
Initial Cost to Company, Land $ 17,200,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 47,918,975      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,101,843      
Gross Amount Carried at close of period 12/31/2020, Land 17,200,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 52,020,818      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 69,220,818      
Accumulated Depreciation (17,674,647)      
Investment in Real Estate, Net 51,546,171      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Dalton, The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Alexandria, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 270      
Initial Cost to Company, Land $ 22,947,777      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 95,334,754      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 95,439      
Gross Amount Carried at close of period 12/31/2020, Land 22,947,777      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 95,430,193      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 118,377,970      
Accumulated Depreciation (7,103,749)      
Investment in Real Estate, Net 111,274,221      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Deerwood (SD)        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Diego, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 316      
Initial Cost to Company, Land $ 2,082,095      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 18,739,815      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 16,342,739      
Gross Amount Carried at close of period 12/31/2020, Land 2,082,095      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 35,082,554      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 37,164,649      
Accumulated Depreciation (31,387,018)      
Investment in Real Estate, Net 5,777,631      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Del Mar Ridge [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Diego, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 181      
Initial Cost to Company, Land $ 7,801,824      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 36,948,176      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,478,037      
Gross Amount Carried at close of period 12/31/2020, Land 7,801,824      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 41,426,213      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 49,228,037      
Accumulated Depreciation (19,145,873)      
Investment in Real Estate, Net 30,082,164      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Eagle Canyon [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Chino Hills, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 252      
Initial Cost to Company, Land $ 1,808,900      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 16,274,361      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 11,453,379      
Gross Amount Carried at close of period 12/31/2020, Land 1,808,900      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 27,727,740      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 29,536,640      
Accumulated Depreciation (21,958,570)      
Investment in Real Estate, Net 7,578,070      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Edgemont at Bethesda Metro [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Bethesda, MD      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 122      
Initial Cost to Company, Land $ 13,092,552      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 43,907,448      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,485,329      
Gross Amount Carried at close of period 12/31/2020, Land 13,092,552      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 46,392,777      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 59,485,329      
Accumulated Depreciation (16,714,861)      
Investment in Real Estate, Net 42,770,468      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Emerson Place [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Boston, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 444      
Initial Cost to Company, Land $ 14,855,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 57,566,636      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 36,095,829      
Gross Amount Carried at close of period 12/31/2020, Land 14,855,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 93,662,465      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 108,517,465      
Accumulated Depreciation (67,775,615)      
Investment in Real Estate, Net 40,741,850      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Encore at Sherman Oaks, The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Sherman Oaks, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 174      
Initial Cost to Company, Land $ 8,700,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 25,446,003      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,521,390      
Gross Amount Carried at close of period 12/31/2020, Land 8,700,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 29,967,393      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 38,667,393      
Accumulated Depreciation (11,941,930)      
Investment in Real Estate, Net 26,725,463      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Edge, The (fka 4885 Edgemoor Lane) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Bethesda, MD      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 52,311,710      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2020, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 52,311,710      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 52,311,710      
Accumulated Depreciation 0      
Investment in Real Estate, Net 52,311,710      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Eviva on Cherokee [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Denver, CO      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 274      
Initial Cost to Company, Land $ 10,507,626      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 100,037,204      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 512,431      
Gross Amount Carried at close of period 12/31/2020, Land 10,507,626      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 100,549,635      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 111,057,261      
Accumulated Depreciation (10,488,698)      
Investment in Real Estate, Net 100,568,563      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Fountains at Emerald Park (fka Emerald Park) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Dublin, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 324      
Initial Cost to Company, Land $ 25,900,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 83,986,217      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,735,333      
Gross Amount Carried at close of period 12/31/2020, Land 25,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 88,721,550      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 114,621,550      
Accumulated Depreciation (28,555,812)      
Investment in Real Estate, Net 86,065,738      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Fremont Center [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Fremont, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 322      
Initial Cost to Company, Land $ 25,800,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 78,753,114      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,103,474      
Gross Amount Carried at close of period 12/31/2020, Land 25,800,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 83,856,588      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 109,656,588      
Accumulated Depreciation (27,673,493)      
Investment in Real Estate, Net 81,983,095      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Gaithersburg Station [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Gaithersburg, MD      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 400      
Initial Cost to Company, Land $ 17,500,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 74,678,917      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,636,691      
Gross Amount Carried at close of period 12/31/2020, Land 17,500,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 79,315,608      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 96,815,608      
Accumulated Depreciation (23,625,030)      
Investment in Real Estate, Net 73,190,578      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Gallery, The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Hermosa Beach, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 169      
Initial Cost to Company, Land $ 18,144,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 46,567,941      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,103,348      
Gross Amount Carried at close of period 12/31/2020, Land 18,144,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 49,671,289      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 67,815,289      
Accumulated Depreciation (26,326,719)      
Investment in Real Estate, Net 41,488,570      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Gateway at Malden Center [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Malden, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 203      
Initial Cost to Company, Land $ 9,209,780      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 25,722,666      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 17,360,595      
Gross Amount Carried at close of period 12/31/2020, Land 9,209,780      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 43,083,261      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 52,293,041      
Accumulated Depreciation (28,698,550)      
Investment in Real Estate, Net 23,594,491      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Geary Court Yard [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Francisco, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 165      
Initial Cost to Company, Land $ 1,722,400      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 15,471,429      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,286,909      
Gross Amount Carried at close of period 12/31/2020, Land 1,722,400      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 21,758,338      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 23,480,738      
Accumulated Depreciation (16,463,219)      
Investment in Real Estate, Net 7,017,519      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Girard [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Boston, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 160      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 102,450,328      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 921,575      
Gross Amount Carried at close of period 12/31/2020, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 103,371,903      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 103,371,903      
Accumulated Depreciation (14,956,283)      
Investment in Real Estate, Net 88,415,620      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Hampshire Place [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 259      
Initial Cost to Company, Land $ 10,806,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 30,335,330      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 8,663,329      
Gross Amount Carried at close of period 12/31/2020, Land 10,806,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 38,998,659      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 49,804,659      
Accumulated Depreciation (21,516,455)      
Investment in Real Estate, Net 28,288,204      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Harbor Steps [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 761      
Initial Cost to Company, Land $ 59,403,601      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 158,829,432      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 43,131,840      
Gross Amount Carried at close of period 12/31/2020, Land 59,403,601      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 201,961,272      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 261,364,873      
Accumulated Depreciation (105,902,659)      
Investment in Real Estate, Net 155,462,214      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Hathaway [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Long Beach, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 385      
Initial Cost to Company, Land $ 2,512,500      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 22,611,912      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 14,527,190      
Gross Amount Carried at close of period 12/31/2020, Land 2,512,500      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 37,139,102      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 39,651,602      
Accumulated Depreciation (28,554,178)      
Investment in Real Estate, Net 11,097,424      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Helios (fka 2nd+Pine) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 398      
Initial Cost to Company, Land $ 18,061,674      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 206,761,817      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 183,520      
Gross Amount Carried at close of period 12/31/2020, Land 18,061,674      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 206,945,337      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 225,007,011      
Accumulated Depreciation (28,336,441)      
Investment in Real Estate, Net 196,670,570      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Heritage at Stone Ridge [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Burlington, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 180      
Initial Cost to Company, Land $ 10,800,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 31,808,335      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,054,858      
Gross Amount Carried at close of period 12/31/2020, Land 10,800,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 34,863,193      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 45,663,193      
Accumulated Depreciation (19,026,623)      
Investment in Real Estate, Net 26,636,570      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Heritage Ridge [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Lynwood, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 197      
Initial Cost to Company, Land $ 6,895,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 18,983,597      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,683,392      
Gross Amount Carried at close of period 12/31/2020, Land 6,895,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 23,666,989      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 30,561,989      
Accumulated Depreciation (12,962,130)      
Investment in Real Estate, Net 17,599,859      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Hesby [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location North Hollywood, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 308      
Initial Cost to Company, Land $ 23,299,892      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 102,700,108      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,406,522      
Gross Amount Carried at close of period 12/31/2020, Land 23,299,892      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 105,106,630      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 128,406,522      
Accumulated Depreciation (28,701,909)      
Investment in Real Estate, Net 99,704,613      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Highlands at South Plainfield [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location South Plainfield, NJ      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 252      
Initial Cost to Company, Land $ 10,080,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 37,526,912      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,930,209      
Gross Amount Carried at close of period 12/31/2020, Land 10,080,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 40,457,121      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 50,537,121      
Accumulated Depreciation (21,704,492)      
Investment in Real Estate, Net 28,832,629      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Hikari [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 128      
Initial Cost to Company, Land $ 9,435,760      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 32,564,240      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,055,340      
Gross Amount Carried at close of period 12/31/2020, Land 9,435,760      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 33,619,580      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 43,055,340      
Accumulated Depreciation (12,719,419)      
Investment in Real Estate, Net 30,335,921      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Hillside ll [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Daly City, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 1,892,874      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2020, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 1,892,874      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 1,892,874      
Accumulated Depreciation 0      
Investment in Real Estate, Net 1,892,874      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Hudson Crossing [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 259      
Initial Cost to Company, Land $ 23,420,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 69,977,699      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,305,385      
Gross Amount Carried at close of period 12/31/2020, Land 23,420,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 73,283,084      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 96,703,084      
Accumulated Depreciation (41,028,871)      
Investment in Real Estate, Net 55,674,213      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Hudson Pointe [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Jersey City, NJ      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 182      
Initial Cost to Company, Land $ 5,350,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 41,114,074      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,258,907      
Gross Amount Carried at close of period 12/31/2020, Land 5,350,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 48,372,981      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 53,722,981      
Accumulated Depreciation (28,021,673)      
Investment in Real Estate, Net 25,701,308      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Huxley, The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Redwood City, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 137      
Initial Cost to Company, Land $ 18,775,028      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 89,336,651      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 38,505      
Gross Amount Carried at close of period 12/31/2020, Land 18,775,028      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 89,375,156      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 108,150,184      
Accumulated Depreciation (7,124,237)      
Investment in Real Estate, Net 101,025,947      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Ivory Wood [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Bothell, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 144      
Initial Cost to Company, Land $ 2,732,800      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 13,888,282      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,964,134      
Gross Amount Carried at close of period 12/31/2020, Land 2,732,800      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 15,852,416      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 18,585,216      
Accumulated Depreciation (9,126,262)      
Investment in Real Estate, Net 9,458,954      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Jia (fka Chinatown Gateway) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 280      
Initial Cost to Company, Land $ 14,791,831      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 78,218,492      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 917,303      
Gross Amount Carried at close of period 12/31/2020, Land 14,791,831      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 79,135,795      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 93,927,626      
Accumulated Depreciation (25,013,639)      
Investment in Real Estate, Net 68,913,987      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Junction 47 (fka West Seattle) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 206      
Initial Cost to Company, Land $ 11,726,305      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 56,584,312      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 256,046      
Gross Amount Carried at close of period 12/31/2020, Land 11,726,305      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 56,840,358      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 68,566,663      
Accumulated Depreciation (12,195,811)      
Investment in Real Estate, Net 56,370,852      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Kelvin, The (fka Modera) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Irvine, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 194      
Initial Cost to Company, Land $ 15,521,552      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 64,853,448      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 778,776      
Gross Amount Carried at close of period 12/31/2020, Land 15,521,552      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 65,632,224      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 81,153,776      
Accumulated Depreciation (15,146,860)      
Investment in Real Estate, Net 66,006,916      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Laguna Clara [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Santa Clara, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 264      
Initial Cost to Company, Land $ 13,642,420      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 31,270,480      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,218,616      
Gross Amount Carried at close of period 12/31/2020, Land 13,642,420      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 38,489,096      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 52,131,516      
Accumulated Depreciation (21,078,780)      
Investment in Real Estate, Net 31,052,736      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Landings at Port Imperial [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location W. New York, NJ      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 276      
Initial Cost to Company, Land $ 27,246,045      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 37,741,050      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 15,622,471      
Gross Amount Carried at close of period 12/31/2020, Land 27,246,045      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 53,363,521      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 80,609,566      
Accumulated Depreciation (35,393,712)      
Investment in Real Estate, Net 45,215,854      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Lane [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 217      
Initial Cost to Company, Land $ 13,142,946      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 71,933,303      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 65,928      
Gross Amount Carried at close of period 12/31/2020, Land 13,142,946      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 71,999,231      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 85,142,177      
Accumulated Depreciation (4,558,633)      
Investment in Real Estate, Net 80,583,544      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Lex, The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Jose, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 387      
Initial Cost to Company, Land $ 21,817,512      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 158,778,598      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 462,150      
Gross Amount Carried at close of period 12/31/2020, Land 21,817,512      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 159,240,748      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 181,058,260      
Accumulated Depreciation (15,000,565)      
Investment in Real Estate, Net 166,057,695      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Liberty Park [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Braintree, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 202      
Initial Cost to Company, Land $ 5,977,504      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 26,749,111      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,808,575      
Gross Amount Carried at close of period 12/31/2020, Land 5,977,504      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 34,557,686      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 40,535,190      
Accumulated Depreciation (21,422,606)      
Investment in Real Estate, Net 19,112,584      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Liberty Tower [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 235      
Initial Cost to Company, Land $ 16,382,822      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 83,817,078      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,517,251      
Gross Amount Carried at close of period 12/31/2020, Land 16,382,822      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 88,334,329      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 104,717,151      
Accumulated Depreciation (34,837,074)      
Investment in Real Estate, Net 69,880,077      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Lincoln Heights [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Quincy, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 336      
Initial Cost to Company, Land $ 5,928,400      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 33,595,262      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 15,212,279      
Gross Amount Carried at close of period 12/31/2020, Land 5,928,400      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 48,807,541      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 54,735,941      
Accumulated Depreciation (39,401,499)      
Investment in Real Estate, Net 15,334,442      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Lofts at Kendall Square (fka Kendall Square) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Cambridge, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 186      
Initial Cost to Company, Land $ 18,696,674      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 78,445,657      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,530,710      
Gross Amount Carried at close of period 12/31/2020, Land 18,696,674      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 85,976,367      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 104,673,041      
Accumulated Depreciation (27,734,674)      
Investment in Real Estate, Net 76,938,367      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Lofts at Kendall Square ll (fka 249 Third Street) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Cambridge, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 84      
Initial Cost to Company, Land $ 4,603,326      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 44,438,432      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures (503)      
Gross Amount Carried at close of period 12/31/2020, Land 4,603,326      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 44,437,929      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 49,041,255      
Accumulated Depreciation (2,109,619)      
Investment in Real Estate, Net 46,931,636      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Longacre House [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 293      
Initial Cost to Company, Land $ 73,170,045      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 53,962,510      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,401,688      
Gross Amount Carried at close of period 12/31/2020, Land 73,170,045      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 59,364,198      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 132,534,243      
Accumulated Depreciation (28,246,752)      
Investment in Real Estate, Net 104,287,491      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Longfellow Place [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Boston, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 710      
Initial Cost to Company, Land $ 38,264,917      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 132,175,915      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 89,681,781      
Gross Amount Carried at close of period 12/31/2020, Land 38,264,917      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 221,857,696      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 260,122,613      
Accumulated Depreciation (163,889,861)      
Investment in Real Estate, Net 96,232,752      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Madox [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Jersey City, NJ      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 131      
Initial Cost to Company, Land $ 9,679,635      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 64,594,205      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 961,691      
Gross Amount Carried at close of period 12/31/2020, Land 9,679,635      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 65,555,896      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 75,235,531      
Accumulated Depreciation (7,494,654)      
Investment in Real Estate, Net 67,740,877      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Mantena [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 98      
Initial Cost to Company, Land $ 22,346,513      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 61,501,158      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,480,793      
Gross Amount Carried at close of period 12/31/2020, Land 22,346,513      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 62,981,951      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 85,328,464      
Accumulated Depreciation (20,145,143)      
Investment in Real Estate, Net 65,183,321      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Marina 41 (fka Marina Del Rey) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Marina Del Rey, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 623      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 168,842,442      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 9,623,804      
Gross Amount Carried at close of period 12/31/2020, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 178,466,246      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 178,466,246      
Accumulated Depreciation (59,646,703)      
Investment in Real Estate, Net 118,819,543      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Mariposa at Playa Del Rey (fka Playa Del Rey) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Playa Del Rey, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 354      
Initial Cost to Company, Land $ 60,900,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 89,311,482      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,039,392      
Gross Amount Carried at close of period 12/31/2020, Land 60,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 96,350,874      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 157,250,874      
Accumulated Depreciation (31,786,197)      
Investment in Real Estate, Net 125,464,677      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Mark on 8th [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 174      
Initial Cost to Company, Land $ 23,004,387      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 51,148,861      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 172,242      
Gross Amount Carried at close of period 12/31/2020, Land 23,004,387      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 51,321,103      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 74,325,490      
Accumulated Depreciation (6,791,552)      
Investment in Real Estate, Net 67,533,938      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Market Street Village [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Diego, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 229      
Initial Cost to Company, Land $ 13,740,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 40,757,301      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,627,968      
Gross Amount Carried at close of period 12/31/2020, Land 13,740,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 43,385,269      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 57,125,269      
Accumulated Depreciation (22,558,686)      
Investment in Real Estate, Net 34,566,583      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Milano Lofts [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 99      
Initial Cost to Company, Land $ 8,125,216      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 27,378,784      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,435,789      
Gross Amount Carried at close of period 12/31/2020, Land 8,125,216      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 31,814,573      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 39,939,789      
Accumulated Depreciation (10,534,953)      
Investment in Real Estate, Net 29,404,836      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Mill Creek [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Milpitas, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 516      
Initial Cost to Company, Land $ 12,858,693      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 57,168,503      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 18,006,191      
Gross Amount Carried at close of period 12/31/2020, Land 12,858,693      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 75,174,694      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 88,033,387      
Accumulated Depreciation (43,305,918)      
Investment in Real Estate, Net 44,727,469      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Mosaic at Metro [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Hyattsville, MD      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 260      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 59,580,898      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,669,692      
Gross Amount Carried at close of period 12/31/2020, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 61,250,590      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 61,250,590      
Accumulated Depreciation (25,749,117)      
Investment in Real Estate, Net 35,501,473      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Mountain View Redevelopment [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Mountain View, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 1,630,338      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2020, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 1,630,338      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 1,630,338      
Accumulated Depreciation 0      
Investment in Real Estate, Net 1,630,338      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Mozaic at Union Station [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 272      
Initial Cost to Company, Land $ 8,500,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 52,529,446      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,595,464      
Gross Amount Carried at close of period 12/31/2020, Land 8,500,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 55,124,910      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 63,624,910      
Accumulated Depreciation (27,902,570)      
Investment in Real Estate, Net 35,722,340      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Murray Hill Tower (fka Murray Hill) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 270      
Initial Cost to Company, Land $ 75,800,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 102,705,401      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 11,586,703      
Gross Amount Carried at close of period 12/31/2020, Land 75,800,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 114,292,104      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 190,092,104      
Accumulated Depreciation (38,926,014)      
Investment in Real Estate, Net 151,166,090      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Next on Sixth [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 398      
Initial Cost to Company, Land $ 52,509,906      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 136,635,650      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 161,352      
Gross Amount Carried at close of period 12/31/2020, Land 52,509,906      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 136,797,002      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 189,306,908      
Accumulated Depreciation (13,325,292)      
Investment in Real Estate, Net 175,981,616      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
North Pier at Harborside [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Jersey City, NJ      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 297      
Initial Cost to Company, Land $ 4,000,159      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 94,290,590      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,943,309      
Gross Amount Carried at close of period 12/31/2020, Land 4,000,159      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 102,233,899      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 106,234,058      
Accumulated Depreciation (57,060,669)      
Investment in Real Estate, Net 49,173,389      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Northglen [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Valencia, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 234      
Initial Cost to Company, Land $ 9,360,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 20,778,553      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,159,183      
Gross Amount Carried at close of period 12/31/2020, Land 9,360,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 27,937,736      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 37,297,736      
Accumulated Depreciation (17,739,770)      
Investment in Real Estate, Net 19,557,966      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Northpark [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Burlingame, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 510      
Initial Cost to Company, Land $ 38,607,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 77,472,217      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 15,619,323      
Gross Amount Carried at close of period 12/31/2020, Land 38,607,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 93,091,540      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 131,698,540      
Accumulated Depreciation (43,765,024)      
Investment in Real Estate, Net 87,933,516      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Notch [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Newcastle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 158      
Initial Cost to Company, Land $ 5,463,324      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 43,490,989      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,378      
Gross Amount Carried at close of period 12/31/2020, Land 5,463,324      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 43,496,367      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 48,959,691      
Accumulated Depreciation (1,267,355)      
Investment in Real Estate, Net 47,692,336      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Oak Park Combined [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Agoura Hills, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 444      
Initial Cost to Company, Land $ 3,390,700      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 30,517,274      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 11,540,745      
Gross Amount Carried at close of period 12/31/2020, Land 3,390,700      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 42,058,019      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 45,448,719      
Accumulated Depreciation (35,268,612)      
Investment in Real Estate, Net 10,180,107      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Oaks [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Santa Clarita, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 520      
Initial Cost to Company, Land $ 23,400,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 61,020,438      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 8,845,874      
Gross Amount Carried at close of period 12/31/2020, Land 23,400,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 69,866,312      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 93,266,312      
Accumulated Depreciation (41,469,709)      
Investment in Real Estate, Net 51,796,603      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Oakwood Crystal City [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 162      
Initial Cost to Company, Land $ 15,400,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 35,474,336      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,223,339      
Gross Amount Carried at close of period 12/31/2020, Land 15,400,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 39,697,675      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 55,097,675      
Accumulated Depreciation (13,360,668)      
Investment in Real Estate, Net 41,737,007      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Ocean Crest [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Solana Beach, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 146      
Initial Cost to Company, Land $ 5,111,200      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 11,910,438      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,063,378      
Gross Amount Carried at close of period 12/31/2020, Land 5,111,200      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 16,973,816      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 22,085,016      
Accumulated Depreciation (12,541,852)      
Investment in Real Estate, Net 9,543,164      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Odin (fka Tallman) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 301      
Initial Cost to Company, Land $ 16,807,519      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 64,519,515      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 95,579      
Gross Amount Carried at close of period 12/31/2020, Land 16,807,519      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 64,615,094      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 81,422,613      
Accumulated Depreciation (13,686,832)      
Investment in Real Estate, Net 67,735,781      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
One Henry Adams [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Francisco, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 241      
Initial Cost to Company, Land $ 30,224,393      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 139,564,405      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 75,093      
Gross Amount Carried at close of period 12/31/2020, Land 30,224,393      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 139,639,498      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 169,863,891      
Accumulated Depreciation (22,296,095)      
Investment in Real Estate, Net 147,567,796      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
One India Street (fka Oakwood Boston) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Boston, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 94      
Initial Cost to Company, Land $ 22,200,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 28,672,979      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,922,941      
Gross Amount Carried at close of period 12/31/2020, Land 22,200,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 35,595,920      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 57,795,920      
Accumulated Depreciation (11,405,705)      
Investment in Real Estate, Net 46,390,215      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Pacific Place [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 430      
Initial Cost to Company, Land $ 32,250,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 110,750,000      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,166,746      
Gross Amount Carried at close of period 12/31/2020, Land 32,250,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 112,916,746      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 145,166,746      
Accumulated Depreciation (35,114,578)      
Investment in Real Estate, Net 110,052,168      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Packard Building [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 61      
Initial Cost to Company, Land $ 5,911,041      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 19,954,959      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,230,863      
Gross Amount Carried at close of period 12/31/2020, Land 5,911,041      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 21,185,822      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 27,096,863      
Accumulated Depreciation (4,881,973)      
Investment in Real Estate, Net 22,214,890      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Parc 77 [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 137      
Initial Cost to Company, Land $ 40,504,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 18,025,679      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,888,757      
Gross Amount Carried at close of period 12/31/2020, Land 40,504,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 24,914,436      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 65,418,436      
Accumulated Depreciation (14,944,137)      
Investment in Real Estate, Net 50,474,299      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Parc Cameron [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 166      
Initial Cost to Company, Land $ 37,600,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 9,855,597      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,768,599      
Gross Amount Carried at close of period 12/31/2020, Land 37,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 17,624,196      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 55,224,196      
Accumulated Depreciation (12,262,578)      
Investment in Real Estate, Net 42,961,618      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Parc Coliseum [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 177      
Initial Cost to Company, Land $ 52,654,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 23,045,751      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 9,759,837      
Gross Amount Carried at close of period 12/31/2020, Land 52,654,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 32,805,588      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 85,459,588      
Accumulated Depreciation (20,290,750)      
Investment in Real Estate, Net 65,168,838      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Parc East Towers [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 324      
Initial Cost to Company, Land $ 102,163,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 108,989,402      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 13,101,902      
Gross Amount Carried at close of period 12/31/2020, Land 102,163,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 122,091,304      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 224,254,304      
Accumulated Depreciation (60,987,908)      
Investment in Real Estate, Net 163,266,396      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Parc on Powell (fka Parkside at Emeryville) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Emeryville, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 173      
Initial Cost to Company, Land $ 16,667,059      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 65,100,751      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 753,908      
Gross Amount Carried at close of period 12/31/2020, Land 16,667,059      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 65,854,659      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 82,521,718      
Accumulated Depreciation (14,664,513)      
Investment in Real Estate, Net 67,857,205      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Park Connecticut [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 142      
Initial Cost to Company, Land $ 13,700,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 59,087,519      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,161,224      
Gross Amount Carried at close of period 12/31/2020, Land 13,700,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 61,248,743      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 74,948,743      
Accumulated Depreciation (18,692,087)      
Investment in Real Estate, Net 56,256,656      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Park West (CA) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 444      
Initial Cost to Company, Land $ 3,033,500      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 27,302,383      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 12,931,215      
Gross Amount Carried at close of period 12/31/2020, Land 3,033,500      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 40,233,598      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 43,267,098      
Accumulated Depreciation (32,562,373)      
Investment in Real Estate, Net 10,704,725      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Parkside [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Union City, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 208      
Initial Cost to Company, Land $ 6,246,700      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 11,827,453      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 8,446,035      
Gross Amount Carried at close of period 12/31/2020, Land 6,246,700      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 20,273,488      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 26,520,188      
Accumulated Depreciation (14,157,450)      
Investment in Real Estate, Net 12,362,738      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Pearl, The (WA) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 80      
Initial Cost to Company, Land $ 6,972,585      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 26,527,415      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,126,346      
Gross Amount Carried at close of period 12/31/2020, Land 6,972,585      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 27,653,761      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 34,626,346      
Accumulated Depreciation (6,325,802)      
Investment in Real Estate, Net 28,300,544      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Pearl MDR (fka Oakwood Marina Del Rey) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Marina Del Rey, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 597      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 120,795,359      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,550,150      
Gross Amount Carried at close of period 12/31/2020, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 127,345,509      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 127,345,509      
Accumulated Depreciation (43,885,705)      
Investment in Real Estate, Net 83,459,804      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Pegasus [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 322      
Initial Cost to Company, Land $ 18,094,052      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 81,905,948      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,302,934      
Gross Amount Carried at close of period 12/31/2020, Land 18,094,052      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 89,208,882      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 107,302,934      
Accumulated Depreciation (35,775,990)      
Investment in Real Estate, Net 71,526,944      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Playa Pacifica [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Hermosa Beach, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 285      
Initial Cost to Company, Land $ 35,100,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 33,473,822      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 24,084,348      
Gross Amount Carried at close of period 12/31/2020, Land 35,100,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 57,558,170      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 92,658,170      
Accumulated Depreciation (34,060,220)      
Investment in Real Estate, Net 58,597,950      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Portofino [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Chino Hills, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 176      
Initial Cost to Company, Land $ 3,572,400      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 14,660,994      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,963,453      
Gross Amount Carried at close of period 12/31/2020, Land 3,572,400      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 18,624,447      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 22,196,847      
Accumulated Depreciation (14,859,876)      
Investment in Real Estate, Net 7,336,971      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Portofino (Val) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Valencia, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 216      
Initial Cost to Company, Land $ 8,640,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 21,487,126      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,277,627      
Gross Amount Carried at close of period 12/31/2020, Land 8,640,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 27,764,753      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 36,404,753      
Accumulated Depreciation (18,614,995)      
Investment in Real Estate, Net 17,789,758      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Portside Towers [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Jersey City, NJ      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 527      
Initial Cost to Company, Land $ 22,487,006      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 96,842,913      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 26,069,539      
Gross Amount Carried at close of period 12/31/2020, Land 22,487,006      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 122,912,452      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 145,399,458      
Accumulated Depreciation (93,853,487)      
Investment in Real Estate, Net 51,545,971      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Potrero 1010 [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Francisco, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 453      
Initial Cost to Company, Land $ 40,830,011      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 181,855,868      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 989,838      
Gross Amount Carried at close of period 12/31/2020, Land 40,830,011      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 182,845,706      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 223,675,717      
Accumulated Depreciation (33,782,465)      
Investment in Real Estate, Net 189,893,252      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Prado (fka Glendale) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Glendale, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 264      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 67,977,313      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,662,673      
Gross Amount Carried at close of period 12/31/2020, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 74,639,986      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 74,639,986      
Accumulated Depreciation (24,014,696)      
Investment in Real Estate, Net 50,625,290      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Prime, The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 281      
Initial Cost to Company, Land $ 34,625,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 77,879,740      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,771,834      
Gross Amount Carried at close of period 12/31/2020, Land 34,625,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 82,651,574      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 117,276,574      
Accumulated Depreciation (35,430,836)      
Investment in Real Estate, Net 81,845,738      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Prism at Park Avenue South (fka 400 Park Aveue South (EQR)) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 269      
Initial Cost to Company, Land $ 76,292,169      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 171,726,887      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 231,618      
Gross Amount Carried at close of period 12/31/2020, Land 76,292,169      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 171,958,505      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 248,250,674      
Accumulated Depreciation (38,979,951)      
Investment in Real Estate, Net 209,270,723      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Promenade at Town Center I & II [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Valencia, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 564      
Initial Cost to Company, Land $ 28,200,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 69,795,915      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 12,726,006      
Gross Amount Carried at close of period 12/31/2020, Land 28,200,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 82,521,921      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 110,721,921      
Accumulated Depreciation (47,521,592)      
Investment in Real Estate, Net 63,200,329      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Providence [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Bothell, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 200      
Initial Cost to Company, Land $ 3,573,621      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 19,055,505      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,058,503      
Gross Amount Carried at close of period 12/31/2020, Land 3,573,621      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 24,114,008      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 27,687,629      
Accumulated Depreciation (13,078,610)      
Investment in Real Estate, Net 14,609,019      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Quarry Hills [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Quincy, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 316      
Initial Cost to Company, Land $ 26,900,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 84,411,162      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,822,863      
Gross Amount Carried at close of period 12/31/2020, Land 26,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 89,234,025      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 116,134,025      
Accumulated Depreciation (28,874,667)      
Investment in Real Estate, Net 87,259,358      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Radius Uptown [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Denver, CO      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 372      
Initial Cost to Company, Land $ 13,644,960      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 121,899,084      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,070,656      
Gross Amount Carried at close of period 12/31/2020, Land 13,644,960      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 122,969,740      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 136,614,700      
Accumulated Depreciation (14,861,159)      
Investment in Real Estate, Net 121,753,541      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Red 160 (fka Redmond Way) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Redmond, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 250      
Initial Cost to Company, Land $ 15,546,376      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 65,320,010      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,554,405      
Gross Amount Carried at close of period 12/31/2020, Land 15,546,376      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 66,874,415      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 82,420,791      
Accumulated Depreciation (22,940,448)      
Investment in Real Estate, Net 59,480,343      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Redmond Court [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Bellevue, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 206      
Initial Cost to Company, Land $ 10,300,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 33,488,745      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,923,709      
Gross Amount Carried at close of period 12/31/2020, Land 10,300,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 35,412,454      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 45,712,454      
Accumulated Depreciation (12,697,765)      
Investment in Real Estate, Net 33,014,689      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Regency Palms [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Huntington Beach, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 310      
Initial Cost to Company, Land $ 1,857,400      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 16,713,254      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 8,166,256      
Gross Amount Carried at close of period 12/31/2020, Land 1,857,400      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 24,879,510      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 26,736,910      
Accumulated Depreciation (20,072,599)      
Investment in Real Estate, Net 6,664,311      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Reserve at Clarendon Centre, The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 252      
Initial Cost to Company, Land $ 10,500,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 52,812,935      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,015,196      
Gross Amount Carried at close of period 12/31/2020, Land 10,500,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 57,828,131      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 68,328,131      
Accumulated Depreciation (34,812,389)      
Investment in Real Estate, Net 33,515,742      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Reserve at Eisenhower, The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Alexandria, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 226      
Initial Cost to Company, Land $ 6,500,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 34,585,060      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,104,139      
Gross Amount Carried at close of period 12/31/2020, Land 6,500,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 39,689,199      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 46,189,199      
Accumulated Depreciation (23,797,415)      
Investment in Real Estate, Net 22,391,784      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Reserve at Empire Lakes [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Rancho Cucamonga, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 467      
Initial Cost to Company, Land $ 16,345,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 73,080,670      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,402,223      
Gross Amount Carried at close of period 12/31/2020, Land 16,345,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 78,482,893      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 94,827,893      
Accumulated Depreciation (41,826,076)      
Investment in Real Estate, Net 53,001,817      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Reserve at Fairfax Corner [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Fairfax, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 652      
Initial Cost to Company, Land $ 15,804,057      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 63,129,051      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 13,200,537      
Gross Amount Carried at close of period 12/31/2020, Land 15,804,057      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 76,329,588      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 92,133,645      
Accumulated Depreciation (47,641,317)      
Investment in Real Estate, Net 44,492,328      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Reserve at Mountain View (fka Mountain View) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Mountain View, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 180      
Initial Cost to Company, Land $ 27,000,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 33,029,605      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,682,065      
Gross Amount Carried at close of period 12/31/2020, Land 27,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 40,711,670      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 67,711,670      
Accumulated Depreciation (14,792,142)      
Investment in Real Estate, Net 52,919,528      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Reserve at Potomac Yard [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Alexandria, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 588      
Initial Cost to Company, Land $ 11,918,917      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 68,862,641      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 18,128,215      
Gross Amount Carried at close of period 12/31/2020, Land 11,918,917      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 86,990,856      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 98,909,773      
Accumulated Depreciation (49,807,938)      
Investment in Real Estate, Net 49,101,835      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Reserve at Town Center I-III (WA) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Mill Creek, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 584      
Initial Cost to Company, Land $ 16,768,705      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 77,623,664      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 9,950,448      
Gross Amount Carried at close of period 12/31/2020, Land 16,768,705      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 87,574,112      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 104,342,817      
Accumulated Depreciation (39,942,888)      
Investment in Real Estate, Net 64,399,929      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Residences at Westgate I (fka Westgate II) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Pasadena, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 252      
Initial Cost to Company, Land $ 17,859,785      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 109,261,438      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 603,327      
Gross Amount Carried at close of period 12/31/2020, Land 17,859,785      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 109,864,765      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 127,724,550      
Accumulated Depreciation (30,747,047)      
Investment in Real Estate, Net 96,977,503      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Residences at Westgate II (fka Westgate III) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Pasadena, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 88      
Initial Cost to Company, Land $ 12,118,248      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 40,486,467      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 119,401      
Gross Amount Carried at close of period 12/31/2020, Land 12,118,248      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 40,605,868      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 52,724,116      
Accumulated Depreciation (9,059,400)      
Investment in Real Estate, Net 43,664,716      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Rianna I & II [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 156      
Initial Cost to Company, Land $ 4,430,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 29,298,096      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,594,173      
Gross Amount Carried at close of period 12/31/2020, Land 4,430,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 30,892,269      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 35,322,269      
Accumulated Depreciation (13,558,016)      
Investment in Real Estate, Net 21,764,253      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Ridgewood Village I&II [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Diego, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 408      
Initial Cost to Company, Land $ 11,809,500      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 34,004,048      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,762,215      
Gross Amount Carried at close of period 12/31/2020, Land 11,809,500      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 40,766,263      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 52,575,763      
Accumulated Depreciation (29,418,122)      
Investment in Real Estate, Net 23,157,641      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Riva Terra I (fka Redwood Shores) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Redwood City, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 304      
Initial Cost to Company, Land $ 34,963,355      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 84,587,658      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 8,097,405      
Gross Amount Carried at close of period 12/31/2020, Land 34,963,355      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 92,685,063      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 127,648,418      
Accumulated Depreciation (31,553,572)      
Investment in Real Estate, Net 96,094,846      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Riva Terra II (fka Harborside) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Redwood City, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 149      
Initial Cost to Company, Land $ 17,136,645      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 40,536,531      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,063,635      
Gross Amount Carried at close of period 12/31/2020, Land 17,136,645      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 44,600,166      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 61,736,811      
Accumulated Depreciation (13,928,284)      
Investment in Real Estate, Net 47,808,527      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Riverpark [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Redmond, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 321      
Initial Cost to Company, Land $ 14,355,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 80,894,049      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,803,736      
Gross Amount Carried at close of period 12/31/2020, Land 14,355,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 85,697,785      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 100,052,785      
Accumulated Depreciation (30,548,447)      
Investment in Real Estate, Net 69,504,338      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Rivington, The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Hoboken, NJ      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 240      
Initial Cost to Company, Land $ 34,340,640      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 112,730,596      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,283,711      
Gross Amount Carried at close of period 12/31/2020, Land 34,340,640      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 116,014,307      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 150,354,947      
Accumulated Depreciation (15,662,554)      
Investment in Real Estate, Net 134,692,393      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Rosecliff II [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Quincy, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 130      
Initial Cost to Company, Land $ 4,922,840      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 30,202,160      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,801,272      
Gross Amount Carried at close of period 12/31/2020, Land 4,922,840      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 32,003,432      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 36,926,272      
Accumulated Depreciation (12,228,816)      
Investment in Real Estate, Net 24,697,456      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Sakura Crossing [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 230      
Initial Cost to Company, Land $ 14,641,990      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 42,858,010      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,561,995      
Gross Amount Carried at close of period 12/31/2020, Land 14,641,990      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 44,420,005      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 59,061,995      
Accumulated Depreciation (17,561,315)      
Investment in Real Estate, Net 41,500,680      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Saxton [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 325      
Initial Cost to Company, Land $ 38,805,400      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 128,652,023      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 373,996      
Gross Amount Carried at close of period 12/31/2020, Land 38,805,400      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 129,026,019      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 167,831,419      
Accumulated Depreciation (9,518,028)      
Investment in Real Estate, Net 158,313,391      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Seventh & James [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 96      
Initial Cost to Company, Land $ 663,800      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 5,974,803      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,639,194      
Gross Amount Carried at close of period 12/31/2020, Land 663,800      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 10,613,997      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 11,277,797      
Accumulated Depreciation (8,600,004)      
Investment in Real Estate, Net 2,677,793      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Sheffield Court [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 597      
Initial Cost to Company, Land $ 3,342,381      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 31,337,332      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 18,847,422      
Gross Amount Carried at close of period 12/31/2020, Land 3,342,381      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 50,184,754      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 53,527,135      
Accumulated Depreciation (41,685,265)      
Investment in Real Estate, Net 11,841,870      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Siena Terrace [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Lake Forest, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 356      
Initial Cost to Company, Land $ 8,900,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 24,083,024      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 8,661,820      
Gross Amount Carried at close of period 12/31/2020, Land 8,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 32,744,844      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 41,644,844      
Accumulated Depreciation (24,001,604)      
Investment in Real Estate, Net 17,643,240      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Skycrest [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Valencia, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 264      
Initial Cost to Company, Land $ 10,560,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 25,574,457      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,581,900      
Gross Amount Carried at close of period 12/31/2020, Land 10,560,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 32,156,357      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 42,716,357      
Accumulated Depreciation (21,036,234)      
Investment in Real Estate, Net 21,680,123      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Skylark [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Union City, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 174      
Initial Cost to Company, Land $ 1,781,600      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 16,731,916      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,763,877      
Gross Amount Carried at close of period 12/31/2020, Land 1,781,600      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 22,495,793      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 24,277,393      
Accumulated Depreciation (16,357,971)      
Investment in Real Estate, Net 7,919,422      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Skyview [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Rancho Santa Margarita, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 260      
Initial Cost to Company, Land $ 3,380,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 21,952,863      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,109,768      
Gross Amount Carried at close of period 12/31/2020, Land 3,380,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 28,062,631      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 31,442,631      
Accumulated Depreciation (20,168,570)      
Investment in Real Estate, Net 11,274,061      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
SoMa II [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Francisco, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 29,406,606      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 5,913,784      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2020, Land 29,406,606      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 5,913,784      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 35,320,390      
Accumulated Depreciation 0      
Investment in Real Estate, Net 35,320,390      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Sonterra at Foothill Ranch [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Foothill Ranch, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 300      
Initial Cost to Company, Land $ 7,503,400      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 24,048,507      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,242,034      
Gross Amount Carried at close of period 12/31/2020, Land 7,503,400      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 30,290,541      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 37,793,941      
Accumulated Depreciation (22,570,636)      
Investment in Real Estate, Net 15,223,305      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
South City Station (fka South San Francisco) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Francisco, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 368      
Initial Cost to Company, Land $ 68,900,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 79,476,861      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,874,314      
Gross Amount Carried at close of period 12/31/2020, Land 68,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 85,351,175      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 154,251,175      
Accumulated Depreciation (27,619,642)      
Investment in Real Estate, Net 126,631,533      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Southwood [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Palo Alto, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 100      
Initial Cost to Company, Land $ 6,936,600      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 14,324,069      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,029,392      
Gross Amount Carried at close of period 12/31/2020, Land 6,936,600      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 21,353,461      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 28,290,061      
Accumulated Depreciation (14,889,800)      
Investment in Real Estate, Net 13,400,261      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Springline [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 136      
Initial Cost to Company, Land $ 9,163,667      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 47,910,981      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 462,653      
Gross Amount Carried at close of period 12/31/2020, Land 9,163,667      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 48,373,634      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 57,537,301      
Accumulated Depreciation (8,167,981)      
Investment in Real Estate, Net 49,369,320      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
STOA [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 237      
Initial Cost to Company, Land $ 25,326,048      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 79,976,031      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 466,898      
Gross Amount Carried at close of period 12/31/2020, Land 25,326,048      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 80,442,929      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 105,768,977      
Accumulated Depreciation (8,160,539)      
Investment in Real Estate, Net 97,608,438      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Summerset Village [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Chatsworth, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 280      
Initial Cost to Company, Land $ 2,890,450      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 23,670,889      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 8,738,634      
Gross Amount Carried at close of period 12/31/2020, Land 2,890,450      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 32,409,523      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 35,299,973      
Accumulated Depreciation (26,387,722)      
Investment in Real Estate, Net 8,912,251      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Summit at Sausalito (fka Sausalito) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Sausalito, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 198      
Initial Cost to Company, Land $ 26,000,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 28,435,024      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 9,988,645      
Gross Amount Carried at close of period 12/31/2020, Land 26,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 38,423,669      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 64,423,669      
Accumulated Depreciation (15,803,477)      
Investment in Real Estate, Net 48,620,192      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Ten23 (fka 500 West 23rd Street) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 111      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 58,881,873      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,160,581      
Gross Amount Carried at close of period 12/31/2020, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 60,042,454      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 60,042,454      
Accumulated Depreciation (18,298,459)      
Investment in Real Estate, Net 41,743,995      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Terraces, The [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Francisco, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 117      
Initial Cost to Company, Land $ 14,087,610      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 16,314,151      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,504,676      
Gross Amount Carried at close of period 12/31/2020, Land 14,087,610      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 18,818,827      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 32,906,437      
Accumulated Depreciation (7,920,298)      
Investment in Real Estate, Net 24,986,139      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Third Square [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Cambridge, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 471      
Initial Cost to Company, Land $ 26,767,171      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 218,822,728      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 9,395,974      
Gross Amount Carried at close of period 12/31/2020, Land 26,767,171      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 228,218,702      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 254,985,873      
Accumulated Depreciation (94,757,814)      
Investment in Real Estate, Net 160,228,059      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Three20 [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 134      
Initial Cost to Company, Land $ 7,030,766      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 29,005,762      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 969,854      
Gross Amount Carried at close of period 12/31/2020, Land 7,030,766      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 29,975,616      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 37,006,382      
Accumulated Depreciation (8,984,046)      
Investment in Real Estate, Net 28,022,336      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Toscana [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Irvine, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 563      
Initial Cost to Company, Land $ 39,410,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 50,806,072      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 25,605,818      
Gross Amount Carried at close of period 12/31/2020, Land 39,410,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 76,411,890      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 115,821,890      
Accumulated Depreciation (48,052,411)      
Investment in Real Estate, Net 67,769,479      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Troy Boston [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Boston, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 378      
Initial Cost to Company, Land $ 34,641,051      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 181,607,331      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,157,467      
Gross Amount Carried at close of period 12/31/2020, Land 34,641,051      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 183,764,798      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 218,405,849      
Accumulated Depreciation (23,789,711)      
Investment in Real Estate, Net 194,616,138      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Urbana (fka Market Street Landing) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 289      
Initial Cost to Company, Land $ 12,542,418      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 75,800,090      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,625,630      
Gross Amount Carried at close of period 12/31/2020, Land 12,542,418      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 78,425,720      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 90,968,138      
Accumulated Depreciation (23,312,467)      
Investment in Real Estate, Net 67,655,671      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Town Square at Mark Center I&II [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Alexandria, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 678      
Initial Cost to Company, Land $ 39,928,464      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 141,208,321      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 14,623,345      
Gross Amount Carried at close of period 12/31/2020, Land 39,928,464      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 155,831,666      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 195,760,130      
Accumulated Depreciation (76,590,730)      
Investment in Real Estate, Net 119,169,400      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Uwajimaya Village [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 176      
Initial Cost to Company, Land $ 8,800,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 22,188,288      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,060,085      
Gross Amount Carried at close of period 12/31/2020, Land 8,800,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 27,248,373      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 36,048,373      
Accumulated Depreciation (13,875,497)      
Investment in Real Estate, Net 22,172,876      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Veloce [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Redmond, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 322      
Initial Cost to Company, Land $ 15,322,724      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 76,176,594      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,058,051      
Gross Amount Carried at close of period 12/31/2020, Land 15,322,724      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 78,234,645      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 93,557,369      
Accumulated Depreciation (25,659,124)      
Investment in Real Estate, Net 67,898,245      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Venue at the Promenade [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Castle Rock, CO      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 312      
Initial Cost to Company, Land $ 8,355,048      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 83,752,689      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 166,209      
Gross Amount Carried at close of period 12/31/2020, Land 8,355,048      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 83,918,898      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 92,273,946      
Accumulated Depreciation (7,716,962)      
Investment in Real Estate, Net 84,556,984      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Verde Condominium Homes (fka Mission Verde, LLC) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Jose, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 108      
Initial Cost to Company, Land $ 5,190,700      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 9,679,109      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,635,959      
Gross Amount Carried at close of period 12/31/2020, Land 5,190,700      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 14,315,068      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 19,505,768      
Accumulated Depreciation (11,286,870)      
Investment in Real Estate, Net 8,218,898      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Veridian (fka Silver Spring) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Silver Spring, MD      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 457      
Initial Cost to Company, Land $ 18,539,817      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 130,407,365      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,297,795      
Gross Amount Carried at close of period 12/31/2020, Land 18,539,817      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 134,705,160      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 153,244,977      
Accumulated Depreciation (53,262,783)      
Investment in Real Estate, Net 99,982,194      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Versailles [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Woodland Hills, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 253      
Initial Cost to Company, Land $ 12,650,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 33,656,292      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 8,575,157      
Gross Amount Carried at close of period 12/31/2020, Land 12,650,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 42,231,449      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 54,881,449      
Accumulated Depreciation (26,065,056)      
Investment in Real Estate, Net 28,816,393      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Versailles (K-Town) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 225      
Initial Cost to Company, Land $ 10,590,975      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 44,409,025      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,913,803      
Gross Amount Carried at close of period 12/31/2020, Land 10,590,975      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 46,322,828      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 56,913,803      
Accumulated Depreciation (20,170,940)      
Investment in Real Estate, Net 36,742,863      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Victor on Venice [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 115      
Initial Cost to Company, Land $ 10,350,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 35,433,437      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,023,741      
Gross Amount Carried at close of period 12/31/2020, Land 10,350,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 37,457,178      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 47,807,178      
Accumulated Depreciation (18,425,633)      
Investment in Real Estate, Net 29,381,545      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Villa Solana [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Laguna Hills, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 272      
Initial Cost to Company, Land $ 1,665,100      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 14,985,678      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 12,946,281      
Gross Amount Carried at close of period 12/31/2020, Land 1,665,100      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 27,931,959      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 29,597,059      
Accumulated Depreciation (23,035,555)      
Investment in Real Estate, Net 6,561,504      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Village at Del Mar Heights, The (fka Del Mar Heights) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Diego, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 168      
Initial Cost to Company, Land $ 15,100,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 40,859,396      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,573,169      
Gross Amount Carried at close of period 12/31/2020, Land 15,100,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 44,432,565      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 59,532,565      
Accumulated Depreciation (15,023,903)      
Investment in Real Estate, Net 44,508,662      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Virginia Square [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 231      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 85,940,003      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,137,694      
Gross Amount Carried at close of period 12/31/2020, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 92,077,697      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 92,077,697      
Accumulated Depreciation (29,622,313)      
Investment in Real Estate, Net 62,455,384      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Vista 99 (fka Tasman) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Jose, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 554      
Initial Cost to Company, Land $ 27,709,329      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 177,555,213      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 840,226      
Gross Amount Carried at close of period 12/31/2020, Land 27,709,329      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 178,395,439      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 206,104,768      
Accumulated Depreciation (33,946,303)      
Investment in Real Estate, Net 172,158,465      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Vista Del Lago [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Mission Viejo, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 608      
Initial Cost to Company, Land $ 4,525,800      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 40,736,293      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 19,765,337      
Gross Amount Carried at close of period 12/31/2020, Land 4,525,800      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 60,501,630      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 65,027,430      
Accumulated Depreciation (52,909,405)      
Investment in Real Estate, Net 12,118,025      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Walden Park [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Cambridge, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 232      
Initial Cost to Company, Land $ 12,448,888      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 52,044,448      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,982,240      
Gross Amount Carried at close of period 12/31/2020, Land 12,448,888      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 57,026,688      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 69,475,576      
Accumulated Depreciation (23,325,875)      
Investment in Real Estate, Net 46,149,701      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Water Park Towers [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 362      
Initial Cost to Company, Land $ 34,400,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 108,485,859      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 10,793,415      
Gross Amount Carried at close of period 12/31/2020, Land 34,400,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 119,279,274      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 153,679,274      
Accumulated Depreciation (39,652,580)      
Investment in Real Estate, Net 114,026,694      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Watertown Square [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Watertown, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 134      
Initial Cost to Company, Land $ 16,800,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 34,074,056      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,904,484      
Gross Amount Carried at close of period 12/31/2020, Land 16,800,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 35,978,540      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 52,778,540      
Accumulated Depreciation (11,625,233)      
Investment in Real Estate, Net 41,153,307      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
West 96th [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 207      
Initial Cost to Company, Land $ 84,800,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 67,055,502      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,658,093      
Gross Amount Carried at close of period 12/31/2020, Land 84,800,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 73,713,595      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 158,513,595      
Accumulated Depreciation (26,104,839)      
Investment in Real Estate, Net 132,408,756      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
West End Apartments (fka Emerson Place/CRP II) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Boston, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 310      
Initial Cost to Company, Land $ 469,546      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 163,123,022      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,461,544      
Gross Amount Carried at close of period 12/31/2020, Land 469,546      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 168,584,566      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 169,054,112      
Accumulated Depreciation (73,099,324)      
Investment in Real Estate, Net 95,954,788      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Westchester at Rockville [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Rockville, MD      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 192      
Initial Cost to Company, Land $ 10,600,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 44,135,207      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,316,004      
Gross Amount Carried at close of period 12/31/2020, Land 10,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 45,451,211      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 56,051,211      
Accumulated Depreciation (14,255,122)      
Investment in Real Estate, Net 41,796,089      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Westmont [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 163      
Initial Cost to Company, Land $ 64,900,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 61,143,259      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,257,673      
Gross Amount Carried at close of period 12/31/2020, Land 64,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 67,400,932      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 132,300,932      
Accumulated Depreciation (21,887,315)      
Investment in Real Estate, Net 110,413,617      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Westside [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 204      
Initial Cost to Company, Land $ 34,200,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 56,962,630      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,357,625      
Gross Amount Carried at close of period 12/31/2020, Land 34,200,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 60,320,255      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 94,520,255      
Accumulated Depreciation (19,197,241)      
Investment in Real Estate, Net 75,323,014      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Westside Barrington (fka Westside Villas III) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 36      
Initial Cost to Company, Land $ 3,060,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 5,538,871      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,182,445      
Gross Amount Carried at close of period 12/31/2020, Land 3,060,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 6,721,316      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 9,781,316      
Accumulated Depreciation (4,457,210)      
Investment in Real Estate, Net 5,324,106      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Westside Barry (Westside Villas VI) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 18      
Initial Cost to Company, Land $ 1,530,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 3,023,523      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 764,582      
Gross Amount Carried at close of period 12/31/2020, Land 1,530,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 3,788,105      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 5,318,105      
Accumulated Depreciation (2,501,385)      
Investment in Real Estate, Net 2,816,720      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Westside Beloit (fka Westside Villas I) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 21      
Initial Cost to Company, Land $ 1,785,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 3,233,254      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 778,767      
Gross Amount Carried at close of period 12/31/2020, Land 1,785,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 4,012,021      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 5,797,021      
Accumulated Depreciation (2,711,404)      
Investment in Real Estate, Net 3,085,617      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Westside Bundy (fka Westside Villas II) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 23      
Initial Cost to Company, Land $ 1,955,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 3,541,435      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 794,239      
Gross Amount Carried at close of period 12/31/2020, Land 1,955,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 4,335,674      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 6,290,674      
Accumulated Depreciation (2,865,440)      
Investment in Real Estate, Net 3,425,234      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Westside Butler (fka Westside Villas IV) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 36      
Initial Cost to Company, Land $ 3,060,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 5,539,390      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,223,921      
Gross Amount Carried at close of period 12/31/2020, Land 3,060,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 6,763,311      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 9,823,311      
Accumulated Depreciation (4,471,969)      
Investment in Real Estate, Net 5,351,342      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Westside Villas (fka Westside Villas V &VII) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 113      
Initial Cost to Company, Land $ 9,605,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 19,983,385      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,909,316      
Gross Amount Carried at close of period 12/31/2020, Land 9,605,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 22,892,701      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 32,497,701      
Accumulated Depreciation (14,993,719)      
Investment in Real Estate, Net 17,503,982      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Windridge (CA) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Laguna Niguel, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 344      
Initial Cost to Company, Land $ 2,662,900      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 23,985,497      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 13,127,981      
Gross Amount Carried at close of period 12/31/2020, Land 2,662,900      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 37,113,478      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 39,776,378      
Accumulated Depreciation (30,933,234)      
Investment in Real Estate, Net 8,843,144      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Wood Creek I [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Pleasant Hill, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 256      
Initial Cost to Company, Land $ 9,729,900      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 23,009,768      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 10,421,107      
Gross Amount Carried at close of period 12/31/2020, Land 9,729,900      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 33,430,875      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 43,160,775      
Accumulated Depreciation (25,852,279)      
Investment in Real Estate, Net 17,308,496      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Woodleaf [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Campbell, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 178      
Initial Cost to Company, Land $ 8,550,600      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 16,988,182      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,182,183      
Gross Amount Carried at close of period 12/31/2020, Land 8,550,600      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 23,170,365      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 31,720,965      
Accumulated Depreciation (17,242,110)      
Investment in Real Estate, Net 14,478,855      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Management Business [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Chicago, IL      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 0      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 138,223,005      
Gross Amount Carried at close of period 12/31/2020, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 138,223,005      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 138,223,005      
Accumulated Depreciation (104,607,870)      
Investment in Real Estate, Net 33,615,135      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Operating Partnership [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Chicago, IL      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 1,543,343      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2020, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 1,543,343      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 1,543,343      
Accumulated Depreciation 0      
Investment in Real Estate, Net 1,543,343      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Other        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location N/A      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 0      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 107,757      
Gross Amount Carried at close of period 12/31/2020, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 107,757      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 107,757      
Accumulated Depreciation (66,902)      
Investment in Real Estate, Net 40,855      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Wholly Owned Unencumbered [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Units | ApartmentUnit 64,363      
Initial Cost to Company, Land $ 4,875,308,605      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 16,033,230,297      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,620,022,325      
Gross Amount Carried at close of period 12/31/2020, Land 4,875,308,605      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 17,653,252,622      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 22,528,561,227      
Accumulated Depreciation (6,521,859,521)      
Investment in Real Estate, Net 16,006,701,706      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
1111 Belle Pre (fka The Madison) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Alexandria, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 360      
Initial Cost to Company, Land $ 18,937,702      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 94,758,679      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 517,009      
Gross Amount Carried at close of period 12/31/2020, Land 18,937,702      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 95,275,688      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 114,213,390      
Accumulated Depreciation (28,767,103)      
Investment in Real Estate, Net 85,446,287      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 86,236,221      
2501 Porter [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 202      
Initial Cost to Company, Land $ 13,000,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 75,271,179      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,046,134      
Gross Amount Carried at close of period 12/31/2020, Land 13,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 82,317,313      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 95,317,313      
Accumulated Depreciation (27,334,401)      
Investment in Real Estate, Net $ 67,982,912      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
300 East 39th (fka East 39th) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 254      
Initial Cost to Company, Land $ 48,900,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 96,174,639      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,841,752      
Gross Amount Carried at close of period 12/31/2020, Land 48,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 102,016,391      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 150,916,391      
Accumulated Depreciation (32,773,924)      
Investment in Real Estate, Net 118,142,467      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 62,517,552      
303 East 83rd (fka Camargue) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 261      
Initial Cost to Company, Land $ 79,400,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 79,122,624      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 10,883,739      
Gross Amount Carried at close of period 12/31/2020, Land 79,400,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 90,006,363      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 169,406,363      
Accumulated Depreciation (30,023,726)      
Investment in Real Estate, Net $ 139,382,637      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
425 Broadway [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Santa Monica, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 101      
Initial Cost to Company, Land $ 12,600,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 34,394,772      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,879,039      
Gross Amount Carried at close of period 12/31/2020, Land 12,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 38,273,811      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 50,873,811      
Accumulated Depreciation (12,637,343)      
Investment in Real Estate, Net $ 38,236,468      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
Alcyone [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 162      
Initial Cost to Company, Land $ 11,379,497      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 49,360,503      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,621,195      
Gross Amount Carried at close of period 12/31/2020, Land 11,379,497      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 50,981,698      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 62,361,195      
Accumulated Depreciation (13,657,401)      
Investment in Real Estate, Net 48,703,794      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 26,717,175      
Artisan Square [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Northridge, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 140      
Initial Cost to Company, Land $ 7,000,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 20,537,359      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,177,087      
Gross Amount Carried at close of period 12/31/2020, Land 7,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 22,714,446      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 29,714,446      
Accumulated Depreciation (13,941,438)      
Investment in Real Estate, Net 15,773,008      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 35,608,719      
Avanti [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Anaheim, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 162      
Initial Cost to Company, Land $ 12,960,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 18,497,682      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,201,662      
Gross Amount Carried at close of period 12/31/2020, Land 12,960,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 22,699,344      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 35,659,344      
Accumulated Depreciation (12,149,740)      
Investment in Real Estate, Net 23,509,604      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 28,029,688      
Avenir Apartments [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Boston, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 241      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 114,321,619      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,957,817      
Gross Amount Carried at close of period 12/31/2020, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 121,279,436      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 121,279,436      
Accumulated Depreciation (36,961,367)      
Investment in Real Estate, Net 84,318,069      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 83,594,553      
Calvert Woodley [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 136      
Initial Cost to Company, Land $ 12,600,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 43,527,379      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,813,918      
Gross Amount Carried at close of period 12/31/2020, Land 12,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 46,341,297      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 58,941,297      
Accumulated Depreciation (14,908,145)      
Investment in Real Estate, Net $ 44,033,152      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
Citrus Suites [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Santa Monica, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 70      
Initial Cost to Company, Land $ 9,000,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 16,950,326      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,159,124      
Gross Amount Carried at close of period 12/31/2020, Land 9,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 19,109,450      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 28,109,450      
Accumulated Depreciation (6,341,008)      
Investment in Real Estate, Net $ 21,768,442      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
City Pointe [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Fullerton, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 183      
Initial Cost to Company, Land $ 6,863,792      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 36,476,208      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,982,736      
Gross Amount Carried at close of period 12/31/2020, Land 6,863,792      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 40,458,944      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 47,322,736      
Accumulated Depreciation (16,998,993)      
Investment in Real Estate, Net 30,323,743      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 39,604,834      
Cleveland House [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 214      
Initial Cost to Company, Land $ 18,300,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 66,392,414      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,478,149      
Gross Amount Carried at close of period 12/31/2020, Land 18,300,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 72,870,563      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 91,170,563      
Accumulated Depreciation (23,146,687)      
Investment in Real Estate, Net $ 68,023,876      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
Columbia Crossing [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 247      
Initial Cost to Company, Land $ 23,500,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 53,045,073      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,332,258      
Gross Amount Carried at close of period 12/31/2020, Land 23,500,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 56,377,331      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 79,877,331      
Accumulated Depreciation (18,786,207)      
Investment in Real Estate, Net $ 61,091,124      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
Elevé [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Glendale, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 208      
Initial Cost to Company, Land $ 14,080,560      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 56,419,440      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,113,113      
Gross Amount Carried at close of period 12/31/2020, Land 14,080,560      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 57,532,553      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 71,613,113      
Accumulated Depreciation (16,339,803)      
Investment in Real Estate, Net 55,273,310      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 38,377,191      
Estancia at Santa Clara (fka Santa Clara) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Santa Clara, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 450      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 123,759,804      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,978,093      
Gross Amount Carried at close of period 12/31/2020, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 126,737,897      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 126,737,897      
Accumulated Depreciation (41,055,149)      
Investment in Real Estate, Net $ 85,682,748      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
Fairchase [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Fairfax, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 392      
Initial Cost to Company, Land $ 23,500,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 87,722,321      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,898,989      
Gross Amount Carried at close of period 12/31/2020, Land 23,500,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 89,621,310      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 113,121,310      
Accumulated Depreciation (27,669,103)      
Investment in Real Estate, Net $ 85,452,207      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
Fairfield [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Stamford, CT      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 263      
Initial Cost to Company, Land $ 6,510,200      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 39,690,120      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 9,558,884      
Gross Amount Carried at close of period 12/31/2020, Land 6,510,200      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 49,249,004      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 55,759,204      
Accumulated Depreciation (38,011,328)      
Investment in Real Estate, Net 17,747,876      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 31,415,078      
Flats at DuPont Circle [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, D.C.      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 306      
Initial Cost to Company, Land $ 35,200,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 108,768,198      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,360,800      
Gross Amount Carried at close of period 12/31/2020, Land 35,200,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 113,128,998      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 148,328,998      
Accumulated Depreciation (33,817,504)      
Investment in Real Estate, Net $ 114,511,494      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
Glo [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 201      
Initial Cost to Company, Land $ 16,047,023      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 48,650,963      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,698,250      
Gross Amount Carried at close of period 12/31/2020, Land 16,047,023      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 52,349,213      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 68,396,236      
Accumulated Depreciation (19,833,118)      
Investment in Real Estate, Net 48,563,118      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 32,536,206      
Heights on Capitol Hill [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 104      
Initial Cost to Company, Land $ 5,425,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 21,138,028      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,918,209      
Gross Amount Carried at close of period 12/31/2020, Land 5,425,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 23,056,237      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 28,481,237      
Accumulated Depreciation (11,613,731)      
Investment in Real Estate, Net 16,867,506      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 22,574,473      
Kelvin Court (fka Alta Pacific) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Irvine, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 132      
Initial Cost to Company, Land $ 10,752,145      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 34,846,856      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 960,195      
Gross Amount Carried at close of period 12/31/2020, Land 10,752,145      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 35,807,051      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 46,559,196      
Accumulated Depreciation (15,665,700)      
Investment in Real Estate, Net 30,893,496      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 26,250,120      
Kenwood Mews [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Burbank, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 141      
Initial Cost to Company, Land $ 14,100,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 24,662,883      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,295,836      
Gross Amount Carried at close of period 12/31/2020, Land 14,100,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 28,958,719      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 43,058,719      
Accumulated Depreciation (16,005,176)      
Investment in Real Estate, Net 27,053,543      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 37,607,274      
La Terrazza at Colma Station [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Colma, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 155      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 41,251,044      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,595,476      
Gross Amount Carried at close of period 12/31/2020, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 44,846,520      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 44,846,520      
Accumulated Depreciation (21,415,715)      
Investment in Real Estate, Net 23,430,805      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 25,018,990      
Lindley Apartments [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Encino, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 129      
Initial Cost to Company, Land $ 5,805,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 25,705,000      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,226,777      
Gross Amount Carried at close of period 12/31/2020, Land 5,805,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 27,931,777      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 33,736,777      
Accumulated Depreciation (11,253,531)      
Investment in Real Estate, Net 22,483,246      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 28,028,542      
Lofts 590 [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Arlington, VA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 212      
Initial Cost to Company, Land $ 20,100,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 67,909,023      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 948,447      
Gross Amount Carried at close of period 12/31/2020, Land 20,100,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 68,857,470      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 88,957,470      
Accumulated Depreciation (20,702,192)      
Investment in Real Estate, Net 68,255,278      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 42,977,538      
Longview Place [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Waltham, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 348      
Initial Cost to Company, Land $ 20,880,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 90,255,509      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 11,851,439      
Gross Amount Carried at close of period 12/31/2020, Land 20,880,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 102,106,948      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 122,986,948      
Accumulated Depreciation (53,169,019)      
Investment in Real Estate, Net 69,817,929      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 84,236,459      
Metro on First [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 102      
Initial Cost to Company, Land $ 8,540,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 12,209,981      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,503,132      
Gross Amount Carried at close of period 12/31/2020, Land 8,540,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 14,713,113      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 23,253,113      
Accumulated Depreciation (7,824,496)      
Investment in Real Estate, Net 15,428,617      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 21,479,983      
Moda [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 251      
Initial Cost to Company, Land $ 12,649,228      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 36,842,012      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 2,077,059      
Gross Amount Carried at close of period 12/31/2020, Land 12,649,228      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 38,919,071      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 51,568,299      
Accumulated Depreciation (16,192,358)      
Investment in Real Estate, Net $ 35,375,941      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
Montierra (CA) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Diego, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 272      
Initial Cost to Company, Land $ 8,160,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 29,360,938      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 8,739,937      
Gross Amount Carried at close of period 12/31/2020, Land 8,160,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 38,100,875      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 46,260,875      
Accumulated Depreciation (27,667,597)      
Investment in Real Estate, Net 18,593,278      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 60,994,469      
Old Town Lofts [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Redmond, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 149      
Initial Cost to Company, Land $ 7,740,467      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 44,146,181      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 911,878      
Gross Amount Carried at close of period 12/31/2020, Land 7,740,467      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 45,058,059      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 52,798,526      
Accumulated Depreciation (10,447,662)      
Investment in Real Estate, Net 42,350,864      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 35,552,619      
Olympus Towers [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 328      
Initial Cost to Company, Land $ 14,752,034      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 73,335,425      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 11,508,550      
Gross Amount Carried at close of period 12/31/2020, Land 14,752,034      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 84,843,975      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 99,596,009      
Accumulated Depreciation (49,773,869)      
Investment in Real Estate, Net 49,822,140      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 94,702,663      
Park Place at San Mateo (fka San Mateo) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Mateo, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 575      
Initial Cost to Company, Land $ 71,900,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 211,907,141      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 14,964,633      
Gross Amount Carried at close of period 12/31/2020, Land 71,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 226,871,774      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 298,771,774      
Accumulated Depreciation (72,984,554)      
Investment in Real Estate, Net $ 225,787,220      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
Skyhouse Denver [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Denver, CO      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 354      
Initial Cost to Company, Land $ 13,562,331      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 126,360,318      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 677,621      
Gross Amount Carried at close of period 12/31/2020, Land 13,562,331      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 127,037,939      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 140,600,270      
Accumulated Depreciation (15,522,629)      
Investment in Real Estate, Net 125,077,641      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 74,151,572      
SoMa Square Apartments (fka South Market) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Francisco, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 410      
Initial Cost to Company, Land $ 79,900,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 177,316,977      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 16,836,498      
Gross Amount Carried at close of period 12/31/2020, Land 79,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 194,153,475      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 274,053,475      
Accumulated Depreciation (60,659,528)      
Investment in Real Estate, Net $ 213,393,947      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
Square One [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 112      
Initial Cost to Company, Land $ 7,222,544      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 26,277,456      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 133,045      
Gross Amount Carried at close of period 12/31/2020, Land 7,222,544      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 26,410,501      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 33,633,045      
Accumulated Depreciation (7,302,057)      
Investment in Real Estate, Net $ 26,330,988      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
Teresina [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Chula Vista, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 440      
Initial Cost to Company, Land $ 28,600,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 61,916,670      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 8,105,506      
Gross Amount Carried at close of period 12/31/2020, Land 28,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 70,022,176      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 98,622,176      
Accumulated Depreciation (36,713,370)      
Investment in Real Estate, Net 61,908,806      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 37,940,000      
Vantage Hollywood [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 298      
Initial Cost to Company, Land $ 42,580,326      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 56,014,674      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,323,418      
Gross Amount Carried at close of period 12/31/2020, Land 42,580,326      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 59,338,092      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 101,918,418      
Accumulated Depreciation (16,037,599)      
Investment in Real Estate, Net 85,880,819      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 38,562,939      
Vintage [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Ontario, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 300      
Initial Cost to Company, Land $ 7,059,230      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 47,677,762      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,982,739      
Gross Amount Carried at close of period 12/31/2020, Land 7,059,230      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 49,660,501      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 56,719,731      
Accumulated Depreciation (25,190,161)      
Investment in Real Estate, Net 31,529,570      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 49,111,234      
Vintage at 425 Broadway (fka Promenade) [Memebr]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Santa Monica, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 60      
Initial Cost to Company, Land $ 9,000,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 13,961,523      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,968,533      
Gross Amount Carried at close of period 12/31/2020, Land 9,000,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 15,930,056      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 24,930,056      
Accumulated Depreciation (5,447,549)      
Investment in Real Estate, Net $ 19,482,507      
Real Estate And Accumulated Depreciation, Encumbrances Reference 0      
West 54th [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location New York, NY      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 222      
Initial Cost to Company, Land $ 60,900,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 48,193,837      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,524,296      
Gross Amount Carried at close of period 12/31/2020, Land 60,900,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 52,718,133      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 113,618,133      
Accumulated Depreciation (18,850,602)      
Investment in Real Estate, Net 94,767,531      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 49,193,451      
Westgate (fka Westgate I) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Pasadena, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 480      
Initial Cost to Company, Land $ 22,898,848      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 133,467,158      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,125,453      
Gross Amount Carried at close of period 12/31/2020, Land 22,898,848      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 137,592,611      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 160,491,459      
Accumulated Depreciation (46,995,276)      
Investment in Real Estate, Net 113,496,183      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 96,433,496      
Portfolio/Entity Encumbrances [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 0      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2020, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 0      
Accumulated Depreciation 0      
Investment in Real Estate, Net 0      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 798,691,865      
Investment in Real Estate - Wholly Owned Encumbered [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Units | ApartmentUnit 10,127      
Initial Cost to Company, Land $ 842,305,927      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 2,668,597,698      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 193,678,425      
Gross Amount Carried at close of period 12/31/2020, Land 842,305,927      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 2,862,276,123      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 3,704,582,050      
Accumulated Depreciation (1,032,587,859)      
Investment in Real Estate, Net 2,671,994,191      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 2,088,144,904      
2300 Elliott [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 92      
Initial Cost to Company, Land $ 796,800      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 7,173,725      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,820,623      
Gross Amount Carried at close of period 12/31/2020, Land 796,800      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 14,994,348      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 15,791,148      
Accumulated Depreciation (12,389,244)      
Investment in Real Estate, Net 3,401,904      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
9th & W [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Washington, DC      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 7,017,002      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2020, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 7,017,002      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 7,017,002      
Accumulated Depreciation 0      
Investment in Real Estate, Net 7,017,002      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Bellevue Meadows [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Bellevue, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 180      
Initial Cost to Company, Land $ 4,507,100      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 12,574,814      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 6,087,865      
Gross Amount Carried at close of period 12/31/2020, Land 4,507,100      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 18,662,679      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 23,169,779      
Accumulated Depreciation (14,585,459)      
Investment in Real Estate, Net 8,584,320      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Canyon Ridge [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Diego, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 162      
Initial Cost to Company, Land $ 4,869,448      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 11,955,063      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,258,637      
Gross Amount Carried at close of period 12/31/2020, Land 4,869,448      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 16,213,700      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 21,083,148      
Accumulated Depreciation (12,460,975)      
Investment in Real Estate, Net 8,622,173      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Country Oaks [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Agoura Hills, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 256      
Initial Cost to Company, Land $ 6,105,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 29,561,865      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,563,839      
Gross Amount Carried at close of period 12/31/2020, Land 6,105,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 37,125,704      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 43,230,704      
Accumulated Depreciation (23,902,034)      
Investment in Real Estate, Net 19,328,670      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Harrison Square (fka Elliot Bay) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Seattle, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 166      
Initial Cost to Company, Land $ 7,600,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 35,844,345      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,832,090      
Gross Amount Carried at close of period 12/31/2020, Land 7,600,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 41,676,435      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 49,276,435      
Accumulated Depreciation (14,608,832)      
Investment in Real Estate, Net 34,667,603      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Lantern Cove [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Foster City, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 232      
Initial Cost to Company, Land $ 6,945,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 23,064,976      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,999,330      
Gross Amount Carried at close of period 12/31/2020, Land 6,945,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 31,064,306      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 38,009,306      
Accumulated Depreciation (21,090,571)      
Investment in Real Estate, Net 16,918,735      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Radius Koreatown [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 301      
Initial Cost to Company, Land $ 32,494,154      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 84,645,202      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 394,749      
Gross Amount Carried at close of period 12/31/2020, Land 32,494,154      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 85,039,951      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 117,534,105      
Accumulated Depreciation (15,147,227)      
Investment in Real Estate, Net 102,386,878      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Rosecliff [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Quincy, MA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 156      
Initial Cost to Company, Land $ 5,460,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 15,721,570      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 4,712,510      
Gross Amount Carried at close of period 12/31/2020, Land 5,460,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 20,434,080      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 25,894,080      
Accumulated Depreciation (14,750,661)      
Investment in Real Estate, Net 11,143,419      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Schooner Bay I [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Foster City, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 168      
Initial Cost to Company, Land $ 5,345,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 20,390,618      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 7,030,910      
Gross Amount Carried at close of period 12/31/2020, Land 5,345,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 27,421,528      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 32,766,528      
Accumulated Depreciation (18,045,457)      
Investment in Real Estate, Net 14,721,071      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Schooner Bay II [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Foster City, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 144      
Initial Cost to Company, Land $ 4,550,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 18,064,764      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 5,732,766      
Gross Amount Carried at close of period 12/31/2020, Land 4,550,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 23,797,530      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 28,347,530      
Accumulated Depreciation (16,050,917)      
Investment in Real Estate, Net 12,296,613      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Surrey Downs [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Bellevue, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 122      
Initial Cost to Company, Land $ 3,057,100      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 7,848,618      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,698,582      
Gross Amount Carried at close of period 12/31/2020, Land 3,057,100      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 11,547,200      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 14,604,300      
Accumulated Depreciation (8,809,623)      
Investment in Real Estate, Net 5,794,677      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Venn at Main [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Bellevue, WA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 350      
Initial Cost to Company, Land $ 26,626,497      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 151,520,448      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 518,736      
Gross Amount Carried at close of period 12/31/2020, Land 26,626,497      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 152,039,184      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 178,665,681      
Accumulated Depreciation (21,480,824)      
Investment in Real Estate, Net 157,184,857      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Virgil Square [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Los Angeles, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 142      
Initial Cost to Company, Land $ 5,500,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 15,216,613      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 3,833,548      
Gross Amount Carried at close of period 12/31/2020, Land 5,500,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 19,050,161      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 24,550,161      
Accumulated Depreciation (10,768,560)      
Investment in Real Estate, Net 13,781,601      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Wood Creek II (fka Willow Brook (CA)) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Pleasant Hill, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 228      
Initial Cost to Company, Land $ 5,055,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 38,388,672      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 9,606,448      
Gross Amount Carried at close of period 12/31/2020, Land 5,055,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 47,995,120      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 53,050,120      
Accumulated Depreciation (27,453,256)      
Investment in Real Estate, Net 25,596,864      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Partially Owned Unencumbered [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Units | ApartmentUnit 2,699      
Initial Cost to Company, Land $ 118,911,099      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 478,988,295      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 75,090,633      
Gross Amount Carried at close of period 12/31/2020, Land 118,911,099      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 554,078,928      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 672,990,027      
Accumulated Depreciation (231,543,640)      
Investment in Real Estate, Net 441,446,387      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 0      
Aero Apartments [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Alameda, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 0      
Initial Cost to Company, Land $ 13,107,242      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 77,932,171      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 0      
Gross Amount Carried at close of period 12/31/2020, Land 13,107,242      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 77,932,171      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 91,039,413      
Accumulated Depreciation 0      
Investment in Real Estate, Net 91,039,413      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 31,493,854      
Canyon Creek (CA) [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location San Ramon, CA      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 268      
Initial Cost to Company, Land $ 5,425,000      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 18,812,120      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 8,138,492      
Gross Amount Carried at close of period 12/31/2020, Land 5,425,000      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 26,950,612      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 32,375,612      
Accumulated Depreciation (19,317,572)      
Investment in Real Estate, Net 13,058,040      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 28,193,080      
Wisconsin Place [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Description Of Location Chevy Chase, MD      
Real Estate And Accumulated Depreciation Units | ApartmentUnit 432      
Initial Cost to Company, Land $ 0      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 172,089,355      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,687,416      
Gross Amount Carried at close of period 12/31/2020, Land 0      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 173,776,771      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 173,776,771      
Accumulated Depreciation (54,348,611)      
Investment in Real Estate, Net 119,428,160      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 146,057,885      
Partially Owned Encumbered [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Units | ApartmentUnit 700      
Initial Cost to Company, Land $ 18,532,242      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 268,833,646      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 9,825,908      
Gross Amount Carried at close of period 12/31/2020, Land 18,532,242      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 278,659,554      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 297,191,796      
Accumulated Depreciation (73,666,183)      
Investment in Real Estate, Net 223,525,613      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 205,744,819      
Total Consolidated Investment in Real Estate [Member]        
Real Estate And Accumulated Depreciation Abstract        
Real Estate And Accumulated Depreciation Units | ApartmentUnit 77,889      
Initial Cost to Company, Land $ 5,855,057,873      
Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements 19,449,649,936      
Real Estate And Accumulated Depreciation Costs Capitalized Subsequent To Acquisition Building And Fixtures 1,898,617,291      
Gross Amount Carried at close of period 12/31/2020, Land 5,855,057,873      
Real Estate And Accumulated Depreciation Carrying Amount Of Buildings And Improvements And Furnitures And Fixtures 21,348,267,227      
Real Estate And Accumulated Depreciation Carrying Amount Of Land And Buildings And Improvements And Furnitures And Fixtures 27,203,325,100      
Accumulated Depreciation (7,859,657,203)      
Investment in Real Estate, Net 19,343,667,897      
SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances $ 2,293,889,723