Real Estate - Schedule of Property Dispositions (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (Loss) on Sale	$ 12,056	$ 5,107	$ 14,070	$ 5,140
Disposal Group, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sale Price			83,850		$ 66,500
Gain (Loss) on Sale	$ 12,056	$ 5,107	$ 14,070	$ 5,140	$ 5,140
Fund III | Disposal Group, Not Discontinued Operations | A3104 M St. Washington D C
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date Sold			Jan. 24, 2019
Sale Price			$ 10,500
Gain (Loss) on Sale			$ 2,014
Fund III | Disposal Group, Not Discontinued Operations | 3780-3858 Nostrand Avenue - New York, NY
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date Sold			Aug. 22, 2019
Sale Price			$ 27,650
Gain (Loss) on Sale			$ 3,079
Fund IV | Disposal Group, Not Discontinued Operations | 210 Bowery - 2 Residential Condos - New York, NY | Scenario One
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date Sold			May 17, 2019
Sale Price			$ 5,900
Gain (Loss) on Sale			$ (242)
Fund IV | Disposal Group, Not Discontinued Operations | 210 Bowery - 2 Residential Condos - New York, NY | Scenario Two
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date Sold			Sep. 23, 2019
Fund IV | Disposal Group, Not Discontinued Operations | JFK Plaza - Waterville, ME
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date Sold			Jul. 24, 2019
Sale Price			$ 7,800
Gain (Loss) on Sale			$ 2,012
Fund IV | Disposal Group, Not Discontinued Operations | 938 W North Avenue - Chicago, IL
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date Sold			Sep. 27, 2019
Sale Price			$ 32,000
Gain (Loss) on Sale			$ 7,207
Fund IV | Disposal Group, Not Discontinued Operations | Lake Montclair
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date Sold					Aug. 27, 2018
Sale Price					$ 22,450
Gain (Loss) on Sale					$ 2,923
Fund IV | Disposal Group, Not Discontinued Operations | 1861 Union Street
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date Sold					Aug. 29, 2018
Sale Price					$ 6,000
Gain (Loss) on Sale					$ 2,184
Fund IV | Disposal Group, Not Discontinued Operations | Bowery4 Residential Condos New York N Y | Scenario One
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date Sold					Nov. 30, 2018
Sale Price					$ 12,050
Fund IV | Disposal Group, Not Discontinued Operations | Bowery4 Residential Condos New York N Y | Scenario Two
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date Sold					Dec. 10, 2018
Fund IV | Disposal Group, Not Discontinued Operations | Bowery4 Residential Condos New York N Y | Scenario Three
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date Sold					Dec. 17, 2018
Fund IV | Disposal Group, Not Discontinued Operations | Bowery4 Residential Condos New York N Y | Scenario Four
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date Sold					Dec. 21, 2018
Fund II | Disposal Group, Not Discontinued Operations | Sherman Avenue
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date Sold					Apr. 17, 2018
Sale Price					$ 26,000
Gain (Loss) on Sale					$ 33