INTEREST INCOME AND INTEREST EXPENSE - Components of Company's Interest Income and Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Interest income
Residential Securities	$ 777,891	$ 662,750	$ 1,487,665	$ 1,442,338
Residential mortgage loans	35,025	18,868	65,016	34,373
Commercial investment portfolio	92,131	79,343	193,083	151,800
Reverse repurchase agreements	22,551	15,845	48,020	27,782
Total interest income	927,598	776,806	1,793,784	1,656,293
Interest expense
Repurchase agreements	683,647	400,475	1,263,161	731,849
Debt issued by securitization vehicles	34,151	18,201	68,358	33,853
Other	32,419	24,016	66,393	44,411
Total interest expense	750,217	442,692	1,397,912	810,113
Net interest income	$ 177,381	$ 334,114	$ 395,872	$ 846,180