REAL ESTATE HELD FOR INVESTMENT - Battery Point Trust Inc. Acquisition (Details) $ in Thousands	Jul. 01, 2020 USD ($) property shares	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Business Acquisition [Line Items]
Total real estate, cost		$ 910,788	$ 824,860
Investments in unconsolidated entities		69,686	78,276
Land
Business Acquisition [Line Items]
Total real estate, cost		193,602	175,317
Buildings and improvements
Business Acquisition [Line Items]
Total real estate, cost		689,202	618,974
Tenant origination and absorption costs
Business Acquisition [Line Items]
Total real estate, cost		$ 27,984	$ 30,569
BPT Holdings, LLC | PORT OP LP | Battery Point
Business Acquisition [Line Items]
Common equity units received in transaction (in units) | shares	510,816
Percent of outstanding common equity units received in transaction	4.50%
Common equity units received in transaction	$ 3,000
Battery Point
Business Acquisition [Line Items]
Shares acquired during period (in shares) | shares	1,000,000
Battery Point | Single-family Home
Business Acquisition [Line Items]
Number of homes | property	559
Battery Point | Single-family Home | Land
Business Acquisition [Line Items]
Total real estate, cost	$ 11,100
Battery Point | Single-family Home | Buildings and improvements
Business Acquisition [Line Items]
Total real estate, cost	44,600
Battery Point | Single-family Home | Tenant origination and absorption costs
Business Acquisition [Line Items]
Total real estate, cost	500
Battery Point | Single-family Home | Series A-3 Preferred Units
Business Acquisition [Line Items]
Number of units, eliminated in consolidation	16,000
Battery Point | Single-family Home | Mortgages | Battery Point Trust Inc. Mortgage Loan
Business Acquisition [Line Items]
Notes payable, net	$ 36,600