DEBT OBLIGATIONS - Schedule of Debt Obligations (Details) - USD ($)	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Outstanding Face Amount	$ 16,076,444,000
Carrying Value	$ 16,050,960,000	$ 35,636,373,000
Weighted Average Funding Cost	2.75%
Weighted Average Life (Years)	1 year 2 months 12 days
MSR purchase price holdback	$ 35,524,000	68,668,000
Repurchase Agreements | Non-Agency RMBS | Retainer Bonds Collateralized by Agency MSRs
Debt Instrument [Line Items]
Carrying Value	508,100,000
Agency RMBS | Repurchase Agreements
Debt Instrument [Line Items]
Outstanding Face Amount	3,897,468,000
Carrying Value	$ 3,897,468,000	15,481,677,000
Weighted Average Funding Cost	0.25%
Weighted Average Life (Years)	1 month 6 days
Agency RMBS | Repurchase Agreements | Collateral
Debt Instrument [Line Items]
Weighted Average Life (Years)	6 years
Outstanding Face of Collateral	$ 3,922,189,000
Amortized Cost Basis of Collateral	4,055,565,000
Carrying Value of Collateral	4,099,159,000
Non-Agency RMBS | Repurchase Agreements | Retained Servicer Advance and Consumer Bonds
Debt Instrument [Line Items]
Carrying Value	6,100,000
Non-Agency RMBS | Repurchase Agreements
Debt Instrument [Line Items]
Outstanding Face Amount	1,934,744,000
Carrying Value	$ 1,932,624,000	7,317,519,000
Weighted Average Funding Cost	4.28%
Weighted Average Life (Years)	2 months 12 days
Non-Agency RMBS | Repurchase Agreements | Collateral
Debt Instrument [Line Items]
Weighted Average Life (Years)	7 years 10 months 24 days
Outstanding Face of Collateral	$ 19,636,467,000
Amortized Cost Basis of Collateral	1,919,715,000
Carrying Value of Collateral	1,890,120,000
Non-Agency RMBS | Repurchase Agreements | Collateral | Retained Servicer Advance and Consumer Bonds
Debt Instrument [Line Items]
Carrying Value	10,000,000.0
Non-Agency RMBS | Repurchase Agreements | Collateral | Retainer Bonds Collateralized by Agency MSRs
Debt Instrument [Line Items]
Carrying Value	650,300,000
Residential Mortgage | Repurchase Agreements
Debt Instrument [Line Items]
Outstanding Face Amount	3,283,186,000
Carrying Value	$ 3,277,727,000	5,053,207,000
Weighted Average Funding Cost	2.95%
Weighted Average Life (Years)	7 months 6 days
Repurchase agreements	$ 283,000,000.0
Interest rate	5.53%
Residential Mortgage | Repurchase Agreements | Collateral
Debt Instrument [Line Items]
Weighted Average Life (Years)	14 years 8 months 12 days
Outstanding Face of Collateral	$ 4,080,121,000
Amortized Cost Basis of Collateral	4,402,356,000
Carrying Value of Collateral	3,779,405,000
Residential Mortgage | Notes Payable
Debt Instrument [Line Items]
Outstanding Face Amount	285,588,000
Carrying Value	$ 281,898,000	864,451,000
Weighted Average Funding Cost	5.40%
Weighted Average Life (Years)	17 years 8 months 12 days
Residential Mortgage | Notes Payable | Collateral
Debt Instrument [Line Items]
Weighted Average Life (Years)	4 years 3 months 18 days
Outstanding Face of Collateral	$ 462,589,000
Amortized Cost Basis of Collateral	493,636,000
Carrying Value of Collateral	444,438,000
Real Estate Owned | Repurchase Agreements
Debt Instrument [Line Items]
Outstanding Face Amount	63,679,000
Carrying Value	$ 63,679,000	63,822,000
Weighted Average Funding Cost	2.37%
Weighted Average Life (Years)	7 months 6 days
Real Estate Owned | Repurchase Agreements | Collateral
Debt Instrument [Line Items]
Carrying Value of Collateral	$ 81,887,000
Total Repurchase Agreements | Repurchase Agreements
Debt Instrument [Line Items]
Outstanding Face Amount	9,179,077,000
Carrying Value	$ 9,171,498,000	27,916,225,000
Weighted Average Funding Cost	2.08%
Weighted Average Life (Years)	3 months 18 days
MSR purchase price holdback	$ 30,300,000
Excess MSRs
Debt Instrument [Line Items]
Carrying Value	294,802,000	217,300,000
Excess MSRs | Notes Payable
Debt Instrument [Line Items]
Outstanding Face Amount	294,802,000
Carrying Value	$ 294,802,000	217,300,000
Weighted Average Funding Cost	4.30%
Weighted Average Life (Years)	1 year 10 months 24 days
Excess MSRs | Notes Payable | Collateral
Debt Instrument [Line Items]
Weighted Average Life (Years)	5 years 7 months 6 days
Outstanding Face of Collateral	$ 90,541,438,000
Amortized Cost Basis of Collateral	49,457,000
Carrying Value of Collateral	54,126,000
MSRs | Notes Payable
Debt Instrument [Line Items]
Outstanding Face Amount	2,700,527,000
Carrying Value	$ 2,691,107,000	2,640,036,000
Weighted Average Funding Cost	3.66%
Weighted Average Life (Years)	1 year 3 months 18 days
MSRs | Notes Payable | Collateral
Debt Instrument [Line Items]
Weighted Average Life (Years)	5 years 8 months 12 days
Outstanding Face of Collateral	$ 399,336,160,000
Amortized Cost Basis of Collateral	4,254,897,000
Carrying Value of Collateral	4,189,180,000
Servicer Advance Investments | Notes Payable
Debt Instrument [Line Items]
Outstanding Face Amount	442,002,000
Carrying Value	$ 442,002,000	581,777,000
Weighted Average Funding Cost	2.92%
Weighted Average Life (Years)	9 months 18 days
Servicer Advance Investments | Notes Payable | Collateral
Debt Instrument [Line Items]
Weighted Average Life (Years)	6 years 3 months 18 days
Outstanding Face of Collateral	$ 467,339,000
Amortized Cost Basis of Collateral	537,388,000
Carrying Value of Collateral	559,011,000
Servicer advances
Debt Instrument [Line Items]
Carrying Value	$ 2,894,933,000	3,181,672,000
Servicer advances | Notes Payable | London Interbank Offered Rate (LIBOR) | Minimum
Debt Instrument [Line Items]
Variable interest rate spread	1.85%
Servicer advances | Notes Payable | London Interbank Offered Rate (LIBOR) | Maximum
Debt Instrument [Line Items]
Variable interest rate spread	2.75%
Servicer advances | Notes Payable
Debt Instrument [Line Items]
Outstanding Face Amount	$ 2,460,854,000
Carrying Value	$ 2,452,931,000	2,599,895,000
Weighted Average Funding Cost	3.59%
Weighted Average Life (Years)	1 year 8 months 12 days
Face amount of debt at fixed rate	$ 1,900,000,000
Servicer advances | Notes Payable | Collateral
Debt Instrument [Line Items]
Weighted Average Life (Years)	8 months 12 days
Outstanding Face of Collateral	$ 2,806,803,000
Amortized Cost Basis of Collateral	2,947,678,000
Carrying Value of Collateral	2,947,678,000
Consumer Loans
Debt Instrument [Line Items]
Carrying Value	716,722,000	816,689,000
Consumer Loans | Notes Payable
Debt Instrument [Line Items]
Outstanding Face Amount	713,594,000
Carrying Value	$ 716,722,000	816,689,000
Weighted Average Funding Cost	3.26%
Weighted Average Life (Years)	3 years 7 months 6 days
Consumer Loans | Notes Payable | Collateral
Debt Instrument [Line Items]
Weighted Average Life (Years)	3 years 8 months 12 days
Outstanding Face of Collateral	$ 712,877,000
Amortized Cost Basis of Collateral	717,877,000
Carrying Value of Collateral	761,456,000
Total Notes Payable | Notes Payable
Debt Instrument [Line Items]
Outstanding Face Amount	6,897,367,000
Carrying Value	$ 6,879,462,000	$ 7,720,148,000
Weighted Average Funding Cost	3.65%
Weighted Average Life (Years)	2 years 4 months 24 days
2.50% Secured Corporate Note | Secured Debt
Debt Instrument [Line Items]
Outstanding Face Amount	$ 83,600,000
2.50% Secured Corporate Note | Secured Debt | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Variable interest rate spread	2.50%
2.75% Secured Corporate Note | Secured Debt | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Outstanding Face Amount	$ 211,200,000
Variable interest rate spread	2.75%
2.25% Agency MSR Secured Note | Secured Debt
Debt Instrument [Line Items]
Outstanding Face Amount	$ 1,474,000,000.0
2.25% Agency MSR Secured Note | Secured Debt | London Interbank Offered Rate (LIBOR) | Minimum
Debt Instrument [Line Items]
Variable interest rate spread	2.25%
2.25% Agency MSR Secured Note | Secured Debt | London Interbank Offered Rate (LIBOR) | Maximum
Debt Instrument [Line Items]
Variable interest rate spread	8.00%
2.50% Agency MSR Secured Note | Secured Debt
Debt Instrument [Line Items]
Outstanding Face Amount	$ 46,100,000
2.50% Agency MSR Secured Note | Secured Debt | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Variable interest rate spread	2.50%
3.55% Corporate Note | Secured Debt
Debt Instrument [Line Items]
Outstanding Face Amount	$ 1,180,400,000
3.55% Corporate Note | Secured Debt | London Interbank Offered Rate (LIBOR) | Minimum
Debt Instrument [Line Items]
Variable interest rate spread	3.55%
3.55% Corporate Note | Secured Debt | London Interbank Offered Rate (LIBOR) | Maximum
Debt Instrument [Line Items]
Variable interest rate spread	4.62%
2.88% Residential Mortgage Loans | Notes Payable | Mr. Cooper
Debt Instrument [Line Items]
Outstanding Face Amount	$ 5,100,000
Collateral amount	$ 1,400,000
2.88% Residential Mortgage Loans | Notes Payable | London Interbank Offered Rate (LIBOR) | Mr. Cooper
Debt Instrument [Line Items]
Variable interest rate spread	2.88%
Non-Agency RMBS | Notes Payable
Debt Instrument [Line Items]
Outstanding Face Amount	$ 92,000,000.0
Non-Agency RMBS | Notes Payable | Maximum
Debt Instrument [Line Items]
Weighted Average Funding Cost	3.76%
6.58% Assetbacked Notes | Secured Debt
Debt Instrument [Line Items]
Outstanding Face Amount	$ 170,500,000
Weighted Average Funding Cost	6.61%
Asset-backed Notes, LIBOR Based Floating Interest Rate | Secured Debt
Debt Instrument [Line Items]
Outstanding Face Amount	$ 18,000,000.0
Collateral amount	$ 900,000
Asset-backed Notes, LIBOR Based Floating Interest Rate | Secured Debt | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Variable interest rate spread	1.25%
Consumer Loan, UPB Class A | Secured Debt
Debt Instrument [Line Items]
Interest rate	3.20%
UPB of Underlying Mortgages	$ 634,500,000
Consumer Loan, UPB Class B | Secured Debt
Debt Instrument [Line Items]
Interest rate	3.58%
UPB of Underlying Mortgages	$ 70,400,000
Consumer Loan, UPB Class C-1 | Secured Debt
Debt Instrument [Line Items]
Interest rate	5.06%
UPB of Underlying Mortgages	$ 8,700,000