REAL ESTATE AND OTHER SECURITIES - Summary of Real Estate Securities (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2023 USD ($) security	Dec. 31, 2022 USD ($)
Debt Securities, Available-for-sale [Line Items]
Outstanding Face Amount	$ 25,859,938
Carrying Value	$ 9,201,474	$ 8,289,277
Weighted Average Life (Years)	1 year
Investments	$ 26,642,155
Residual Bonds
Debt Securities, Available-for-sale [Line Items]
Investments	17,800
Non-Agency Bonds
Debt Securities, Available-for-sale [Line Items]
Investments	800
AFS Agency
Debt Securities, Available-for-sale [Line Items]
Outstanding Face Amount	75,928
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Carrying Value	$ 65,093	73,439
Number of Securities | security	1
Weighted Average Coupon	3.50%
Weighted Average Yield	3.50%
Weighted Average Life (Years)	10 years 10 months 24 days
AFS Non-Agency
Debt Securities, Available-for-sale [Line Items]
Outstanding Face Amount	$ 2,516,651
Gross Unrealized Gains	72,278
Gross Unrealized Losses	(32,923)
Carrying Value	$ 366,972	397,076
Number of Securities | security	333
Weighted Average Coupon	3.50%
Weighted Average Yield	3.90%
Weighted Average Life (Years)	5 years 6 months
FVO Agency
Debt Securities, Available-for-sale [Line Items]
Outstanding Face Amount	$ 8,655,669
Gross Unrealized Gains	0
Gross Unrealized Losses	(253,951)
Carrying Value	$ 8,235,153	7,264,978
Number of Securities | security	44
Weighted Average Coupon	5.20%
Weighted Average Yield	5.20%
Weighted Average Life (Years)	9 years 7 months 6 days
FVO Non-Agency
Debt Securities, Available-for-sale [Line Items]
Outstanding Face Amount	$ 14,611,690
Gross Unrealized Gains	59,989
Gross Unrealized Losses	(97,944)
Carrying Value	$ 534,256	553,784
Number of Securities | security	354
Weighted Average Coupon	2.90%
Weighted Average Yield	6.60%
Weighted Average Life (Years)	8 years 1 month 6 days
Agency And Non-Agency Residential Mortgage Backed Securities
Debt Securities, Available-for-sale [Line Items]
Outstanding Face Amount	$ 25,859,938
Gross Unrealized Gains	132,267
Gross Unrealized Losses	(384,818)
Carrying Value	$ 9,201,474	$ 8,289,277
Number of Securities | security	732
Weighted Average Coupon	5.20%
Weighted Average Yield	5.20%
Weighted Average Life (Years)	9 years 10 months 24 days
Agency
Debt Securities, Available-for-sale [Line Items]
Outstanding Face Amount	$ 8,731,597
Agency | Fixed Rate Securities
Debt Securities, Available-for-sale [Line Items]
Outstanding Face Amount	8,700,000
Non-Agency
Debt Securities, Available-for-sale [Line Items]
Outstanding Face Amount	17,128,341
Non-Agency | Fixed Rate Securities
Debt Securities, Available-for-sale [Line Items]
Outstanding Face Amount	7,900,000
Residual and interest - only notional amount	7,000,000
Non-Agency | Floating Rate Securities
Debt Securities, Available-for-sale [Line Items]
Outstanding Face Amount	9,200,000
Residual and interest - only notional amount	9,000,000
Corporate debt
Debt Securities, Available-for-sale [Line Items]
Outstanding Face Amount	514
Gross Unrealized Gains	3
Gross Unrealized Losses	0
Carrying Value	$ 512
Number of Securities | security	2
Weighted Average Coupon	8.20%
Weighted Average Yield	9.50%
Weighted Average Life (Years)	1 year 6 months
Consumer loan bonds
Debt Securities, Available-for-sale [Line Items]
Outstanding Face Amount	$ 301
Gross Unrealized Gains	663
Gross Unrealized Losses	0
Carrying Value	$ 663
Number of Securities | security	2
Weighted Average Life (Years)	1 month 6 days
Interest-only securities
Debt Securities, Available-for-sale [Line Items]
Outstanding Face Amount	$ 9,247,297
Gross Unrealized Gains	33,197
Gross Unrealized Losses	(31,955)
Carrying Value	$ 139,108
Number of Securities | security	145
Weighted Average Coupon	0.80%
Weighted Average Yield	9.50%
Weighted Average Life (Years)	2 years 4 months 24 days
Servicing strips
Debt Securities, Available-for-sale [Line Items]
Outstanding Face Amount	$ 4,087,218
Gross Unrealized Gains	17,726
Gross Unrealized Losses	(3,734)
Carrying Value	$ 50,737
Number of Securities | security	61
Weighted Average Coupon	0.20%
Weighted Average Yield	15.20%
Weighted Average Life (Years)	3 years 10 months 24 days
Commercial Mortgage Backed Securities
Debt Securities, Available-for-sale [Line Items]
Outstanding Face Amount	$ 3,931
Gross Unrealized Gains	103
Gross Unrealized Losses	0
Carrying Value	$ 3,900
Number of Securities | security	2
Weighted Average Coupon	7.90%
Weighted Average Yield	8.80%
Weighted Average Life (Years)	1 year 7 months 6 days