SEGMENT REPORTING - Segment Assets and Accumulated Depreciation (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Segment Reporting Information [Line Items]
Property owned	$ 1,838,837	$ 1,812,557
Less accumulated depreciation	(407,400)	(399,249)
Total property owned	1,431,437	1,413,308
Mortgage loans receivable at fair value	37,457	24,661
Cash and cash equivalents	5,194	392	$ 52,714
Restricted cash	8,444	6,918	$ 2,535
Other assets	17,218	18,904
TOTAL ASSETS	1,499,750	1,464,183
Multifamily
Segment Reporting Information [Line Items]
Property owned	1,805,592	1,727,229
Less accumulated depreciation	(395,716)	(368,717)
Total property owned	1,409,876	1,358,512
All Other
Segment Reporting Information [Line Items]
Property owned	33,245	85,328
Less accumulated depreciation	(11,684)	(30,532)
Total property owned	$ 21,561	$ 54,796