OTHER ASSETS AND LIABILITIES, GENERAL AND ADMINISTRATIVE, AND OTHER ITEMS - Real Estate Owned (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021 USD ($)
REO
Beginning balance	$ 45,299
Purchases	2,644
Transfer of loans to REO	8,701
Sales	(23,817)
Depreciation	0
Valuation (provision) reversal	3,157
Ending balance	35,984
SFR
Beginning balance	41,271
Purchases	72,379
Transfer of loans to REO	0
Sales	(127)
Depreciation	(371)
Valuation (provision) reversal	0
Ending balance	113,152
Early buy-out and reverse mortgage loans, foreclosure completed
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Claims receivable	13,700
Residential Mortgage Loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Unpaid principal balance	$ 302,200