Real Estate - Schedule of Property Dispositions (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (Loss) on Sale	$ 485	$ 485	$ 2,014
Disposed of by sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sale Price		15,250
Gain (Loss) on Sale		485
Disposal Group, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sale Price				$ 109,326
Gain (Loss) on Sale	$ 485	$ 485	$ 2,014	$ 30,324
Fund IV | Disposed of by sale | Colonie Plaza - Albany, NY
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date Sold		Apr. 13, 2020
Sale Price		$ 15,250
Gain (Loss) on Sale		$ 485
Fund IV | Disposal Group, Not Discontinued Operations | 210 Bowery - 3 Residential Condos - New York, NY
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date Sold				Nov. 07, 2019
Fund IV | Disposal Group, Not Discontinued Operations | 210 Bowery - 3 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				$ 8,826
Gain (Loss) on Sale				$ (242)
Fund IV | Disposal Group, Not Discontinued Operations | 210 Bowery - 3 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				$ 2,075
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				$ 7,144
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				$ 2,562
Core Portfolio | Disposal Group, Not Discontinued Operations | Pacesetter Park
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Date Sold				Oct. 28, 2019
Sale Price				$ 22,550
Gain (Loss) on Sale				$ 16,771