REAL ESTATE HELD FOR INVESTMENT - Schedule of Real Estate Investments (Details) - USD ($) $ in Thousands			9 Months Ended
	Jan. 08, 2019	Sep. 07, 2016	Sep. 30, 2020	Dec. 31, 2019
Real Estate Properties [Line Items]
Total real estate, cost			$ 910,788	$ 824,860
Accumulated depreciation and amortization			(88,290)	(65,381)
Total real estate, net			$ 822,498	759,479
Investment in PORT II OP LP
Real Estate Properties [Line Items]
Ownership %			96.10%
Preferred Class A | Subsidiary of Common Parent
Real Estate Properties [Line Items]
Non-voting preferred membership units sold		820
Interest rate on Class A non-voting preferred membership units		10.00%
Proceeds from sale of units		$ 800
Preferred Class A-2 | Subsidiary of Common Parent
Real Estate Properties [Line Items]
Non-voting preferred membership units sold	1,927
Interest rate on Class A non-voting preferred membership units	10.00%
Proceeds from sale of units	$ 1,900
Total Richardson Portfolio
Real Estate Properties [Line Items]
Total real estate, cost			$ 47,711
Accumulated depreciation and amortization			(13,450)
Total real estate, net			$ 34,261
Palisades Central I
Real Estate Properties [Line Items]
Date Acquired or Foreclosed on			Nov. 23, 2011
Total real estate, cost			$ 14,072
Accumulated depreciation and amortization			(4,194)
Total real estate, net			$ 9,878
Ownership %			90.00%
Palisades Central II
Real Estate Properties [Line Items]
Date Acquired or Foreclosed on			Nov. 23, 2011
Total real estate, cost			$ 22,826
Accumulated depreciation and amortization			(6,496)
Total real estate, net			$ 16,330
Ownership %			90.00%
Greenway I
Real Estate Properties [Line Items]
Date Acquired or Foreclosed on			Nov. 23, 2011
Total real estate, cost			$ 3,017
Accumulated depreciation and amortization			(1,176)
Total real estate, net			$ 1,841
Ownership %			90.00%
Greenway III
Real Estate Properties [Line Items]
Date Acquired or Foreclosed on			Nov. 23, 2011
Total real estate, cost			$ 4,662
Accumulated depreciation and amortization			(1,584)
Total real estate, net			$ 3,078
Ownership %			90.00%
Undeveloped Land
Real Estate Properties [Line Items]
Date Acquired or Foreclosed on			Nov. 23, 2011
Total real estate, cost			$ 3,134
Accumulated depreciation and amortization			0
Total real estate, net			$ 3,134
Ownership %			90.00%
Park Highlands
Real Estate Properties [Line Items]
Date Acquired or Foreclosed on			Dec. 30, 2011
Total real estate, cost			$ 36,817
Accumulated depreciation and amortization			0
Total real estate, net			$ 36,817
Ownership %			100.00%
Park Centre
Real Estate Properties [Line Items]
Date Acquired or Foreclosed on			Mar. 28, 2013
Total real estate, cost			$ 38,017
Accumulated depreciation and amortization			(8,066)
Total real estate, net			$ 29,951
Ownership %			100.00%
1180 Raymond
Real Estate Properties [Line Items]
Date Acquired or Foreclosed on			Aug. 20, 2013
Total real estate, cost			$ 47,523
Accumulated depreciation and amortization			(8,857)
Total real estate, net			$ 38,666
Ownership %			100.00%
Park Highlands II
Real Estate Properties [Line Items]
Date Acquired or Foreclosed on			Dec. 10, 2013
Total real estate, cost			$ 27,854
Accumulated depreciation and amortization			0
Total real estate, net			$ 27,854
Ownership %			100.00%
Richardson Land II
Real Estate Properties [Line Items]
Date Acquired or Foreclosed on			Sep. 04, 2014
Total real estate, cost			$ 3,418
Accumulated depreciation and amortization			0
Total real estate, net			$ 3,418
Ownership %			90.00%
Crown Pointe
Real Estate Properties [Line Items]
Date Acquired or Foreclosed on			Feb. 14, 2017
Total real estate, cost			$ 95,871
Accumulated depreciation and amortization			(13,987)
Total real estate, net			$ 81,884
Ownership %			100.00%
The Marq
Real Estate Properties [Line Items]
Date Acquired or Foreclosed on			Mar. 01, 2018
Total real estate, cost			$ 95,914
Accumulated depreciation and amortization			(9,618)
Total real estate, net			$ 86,296
Ownership %			100.00%
City Tower
Real Estate Properties [Line Items]
Date Acquired or Foreclosed on			Mar. 06, 2018
Total real estate, cost			$ 158,423
Accumulated depreciation and amortization			(16,780)
Total real estate, net			$ 141,643
Ownership %			100.00%
Eight & Nine Corporate Centre
Real Estate Properties [Line Items]
Date Acquired or Foreclosed on			Jun. 08, 2018
Total real estate, cost			$ 79,930
Accumulated depreciation and amortization			(6,639)
Total real estate, net			$ 73,291
Ownership %			100.00%
Georgia 400 Center
Real Estate Properties [Line Items]
Date Acquired or Foreclosed on			May 23, 2019
Total real estate, cost			$ 92,640
Accumulated depreciation and amortization			(6,426)
Total real estate, net			$ 86,214
Ownership %			100.00%
Single-Family Homes Portfolio
Real Estate Properties [Line Items]
Total real estate, cost			$ 186,670
Accumulated depreciation and amortization			(4,467)
Total real estate, net			$ 182,203
Ownership %			96.10%
Land
Real Estate Properties [Line Items]
Total real estate, cost			$ 193,602	175,317
Land | Total Richardson Portfolio
Real Estate Properties [Line Items]
Total real estate, cost			6,244
Land | Palisades Central I
Real Estate Properties [Line Items]
Total real estate, cost			1,037
Land | Palisades Central II
Real Estate Properties [Line Items]
Total real estate, cost			810
Land | Greenway I
Real Estate Properties [Line Items]
Total real estate, cost			561
Land | Greenway III
Real Estate Properties [Line Items]
Total real estate, cost			702
Land | Undeveloped Land
Real Estate Properties [Line Items]
Total real estate, cost			3,134
Land | Park Highlands
Real Estate Properties [Line Items]
Total real estate, cost			36,817
Land | Park Centre
Real Estate Properties [Line Items]
Total real estate, cost			3,251
Land | 1180 Raymond
Real Estate Properties [Line Items]
Total real estate, cost			8,292
Land | Park Highlands II
Real Estate Properties [Line Items]
Total real estate, cost			27,854
Land | Richardson Land II
Real Estate Properties [Line Items]
Total real estate, cost			3,418
Land | Crown Pointe
Real Estate Properties [Line Items]
Total real estate, cost			22,590
Land | The Marq
Real Estate Properties [Line Items]
Total real estate, cost			10,387
Land | City Tower
Real Estate Properties [Line Items]
Total real estate, cost			13,930
Land | Eight & Nine Corporate Centre
Real Estate Properties [Line Items]
Total real estate, cost			17,401
Land | Georgia 400 Center
Real Estate Properties [Line Items]
Total real estate, cost			11,431
Land | Single-Family Homes Portfolio
Real Estate Properties [Line Items]
Total real estate, cost			31,987
Buildings and improvements
Real Estate Properties [Line Items]
Total real estate, cost			689,202	618,974
Buildings and improvements | Total Richardson Portfolio
Real Estate Properties [Line Items]
Total real estate, cost			41,467
Buildings and improvements | Palisades Central I
Real Estate Properties [Line Items]
Total real estate, cost			13,035
Buildings and improvements | Palisades Central II
Real Estate Properties [Line Items]
Total real estate, cost			22,016
Buildings and improvements | Greenway I
Real Estate Properties [Line Items]
Total real estate, cost			2,456
Buildings and improvements | Greenway III
Real Estate Properties [Line Items]
Total real estate, cost			3,960
Buildings and improvements | Undeveloped Land
Real Estate Properties [Line Items]
Total real estate, cost			0
Buildings and improvements | Park Highlands
Real Estate Properties [Line Items]
Total real estate, cost			0
Buildings and improvements | Park Centre
Real Estate Properties [Line Items]
Total real estate, cost			34,766
Buildings and improvements | 1180 Raymond
Real Estate Properties [Line Items]
Total real estate, cost			39,231
Buildings and improvements | Park Highlands II
Real Estate Properties [Line Items]
Total real estate, cost			0
Buildings and improvements | Richardson Land II
Real Estate Properties [Line Items]
Total real estate, cost			0
Buildings and improvements | Crown Pointe
Real Estate Properties [Line Items]
Total real estate, cost			69,663
Buildings and improvements | The Marq
Real Estate Properties [Line Items]
Total real estate, cost			81,976
Buildings and improvements | City Tower
Real Estate Properties [Line Items]
Total real estate, cost			137,780
Buildings and improvements | Eight & Nine Corporate Centre
Real Estate Properties [Line Items]
Total real estate, cost			58,011
Buildings and improvements | Georgia 400 Center
Real Estate Properties [Line Items]
Total real estate, cost			73,841
Buildings and improvements | Single-Family Homes Portfolio
Real Estate Properties [Line Items]
Total real estate, cost			152,467
Tenant origination and absorption costs
Real Estate Properties [Line Items]
Total real estate, cost			27,984	$ 30,569
Tenant origination and absorption costs | Total Richardson Portfolio
Real Estate Properties [Line Items]
Total real estate, cost			0
Tenant origination and absorption costs | Palisades Central I
Real Estate Properties [Line Items]
Total real estate, cost			0
Tenant origination and absorption costs | Palisades Central II
Real Estate Properties [Line Items]
Total real estate, cost			0
Tenant origination and absorption costs | Greenway I
Real Estate Properties [Line Items]
Total real estate, cost			0
Tenant origination and absorption costs | Greenway III
Real Estate Properties [Line Items]
Total real estate, cost			0
Tenant origination and absorption costs | Undeveloped Land
Real Estate Properties [Line Items]
Total real estate, cost			0
Tenant origination and absorption costs | Park Highlands
Real Estate Properties [Line Items]
Total real estate, cost			0
Tenant origination and absorption costs | Park Centre
Real Estate Properties [Line Items]
Total real estate, cost			0
Tenant origination and absorption costs | 1180 Raymond
Real Estate Properties [Line Items]
Total real estate, cost			0
Tenant origination and absorption costs | Park Highlands II
Real Estate Properties [Line Items]
Total real estate, cost			0
Tenant origination and absorption costs | Richardson Land II
Real Estate Properties [Line Items]
Total real estate, cost			0
Tenant origination and absorption costs | Crown Pointe
Real Estate Properties [Line Items]
Total real estate, cost			3,618
Tenant origination and absorption costs | The Marq
Real Estate Properties [Line Items]
Total real estate, cost			3,551
Tenant origination and absorption costs | City Tower
Real Estate Properties [Line Items]
Total real estate, cost			6,713
Tenant origination and absorption costs | Eight & Nine Corporate Centre
Real Estate Properties [Line Items]
Total real estate, cost			4,518
Tenant origination and absorption costs | Georgia 400 Center
Real Estate Properties [Line Items]
Total real estate, cost			7,368
Tenant origination and absorption costs | Single-Family Homes Portfolio
Real Estate Properties [Line Items]
Total real estate, cost			$ 2,216