TRANSACTIONS WITH AFFILIATES AND AFFILIATED ENTITIES - Narrative (Details) $ / shares in Units, $ in Thousands				1 Months Ended	3 Months Ended	12 Months Ended
	Sep. 14, 2021 shares	Apr. 14, 2021 shares	May 19, 2020 USD ($) $ / shares shares	Mar. 31, 2020 USD ($) purchaser	Jun. 30, 2020 shares	Dec. 31, 2021 USD ($) $ / shares shares	Dec. 31, 2020 $ / shares shares
Related Party Transaction [Line Items]
Management agreement, renewal term (in years)						1 year
Termination fee, number of months' pay (in months)						12 months
Proportion of directors' votes needed to terminate						0.6667
Number of purchasers | purchaser				6
Owned mortgages, mortgage-based and asset-backed securities at fair value				$ 6,100,000
Proceeds from sale of mortgage-backed securities				3,300,000
Options granted (in shares) | shares						7,051,335	1,619,739
Common stock, par value (in dollars per share) | $ / shares			$ 0.01			$ 0.01	$ 0.01
Face amount of debt						$ 29,273,486
Share-based Payment Arrangement, Nonemployee
Related Party Transaction [Line Items]
Options granted (in shares) | shares	1,900,000	5,200,000
Warrant | Share-based Payment Arrangement, Nonemployee
Related Party Transaction [Line Items]
Options granted (in shares) | shares			43,400,000		43,400,000
Percentage of lenders and recipients managed by an affiliate of the manager			0.48
2020 Term Loan
Related Party Transaction [Line Items]
Debt instrument, term			3 years
Principal amount			$ 600,000
Fortress Purchaser
Related Party Transaction [Line Items]
Owned mortgages, mortgage-based and asset-backed securities at fair value				1,850,000
Payments to acquire mortgage-backed securities				$ 1,000,000
Manager
Related Party Transaction [Line Items]
Management fee rate (percent)						1.50%
Incentive compensation percentage						25.00%
Interest rate for incentive compensation						10.00%
Affiliate of Manager | Senior Loans
Related Party Transaction [Line Items]
Interest rate, stated percentage						10.50%
Face amount of debt						$ 174,600
Affiliate of Manager | Senior Subordinated Loans
Related Party Transaction [Line Items]
Interest rate, stated percentage						16.00%
Face amount of debt						$ 54,100