INTEREST INCOME AND INTEREST EXPENSE - Components of Company's Interest Income and Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Interest income
Residential securities	$ 644,634	$ 410,380
Residential mortgage loans	37,109	47,557
Commercial investment portfolio	81,601	95,676
Reverse repurchase agreements	34	1,413
Total interest income	763,378	555,026
Interest expense
Repurchase agreements	42,585	434,021
Debt issued by securitization vehicles	26,276	42,119
Participations issued	597	0
Other	6,515	27,333
Total interest expense	75,973	503,473
Net interest income	$ 687,405	$ 51,553