DEBT OBLIGATIONS - Schedule of Debt Obligations (Details) - USD ($)	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Outstanding Face Amount	$ 30,524,956,000
Carrying Value	$ 30,516,231,000	$ 22,656,235,000
Weighted Average Funding Cost	3.08%
Weighted Average Life (Years)	24 days
MSR purchase price holdback	$ 80,892,000	49,352,000
Agency RMBS | Repurchase Agreements
Debt Instrument [Line Items]
Outstanding Face Amount	10,733,236,000
Carrying Value	$ 10,733,236,000	4,346,070,000
Weighted Average Funding Cost	2.31%
Weighted Average Life (Years)	3 days
Agency RMBS | Repurchase Agreements | Trade And Other Receivables
Debt Instrument [Line Items]
Collateral amount	$ 4,400,000,000
Agency RMBS | Repurchase Agreements | Collateral
Debt Instrument [Line Items]
Weighted Average Life (Years)	2 years 4 months 24 days
Outstanding Face of Collateral	$ 10,611,553,000
Amortized Cost Basis of Collateral	10,825,984,000
Carrying Value of Collateral	10,886,787,000
Non-Agency RMBS | Repurchase Agreements
Debt Instrument [Line Items]
Outstanding Face Amount	7,144,329,000
Carrying Value	$ 7,144,329,000	7,434,785,000
Weighted Average Funding Cost	3.08%
Weighted Average Life (Years)	3 days
Non-Agency RMBS | Repurchase Agreements | Retained Servicer Advance and Consumer Bonds
Debt Instrument [Line Items]
Carrying Value	$ 7,500,000
Non-Agency RMBS | Repurchase Agreements | Retainer Bonds Collateralized by Agency MSRs
Debt Instrument [Line Items]
Carrying Value	$ 671,300,000
Non-Agency RMBS | Repurchase Agreements | Collateral
Debt Instrument [Line Items]
Weighted Average Life (Years)	6 years 3 months 18 days
Outstanding Face of Collateral	$ 21,021,981,000
Amortized Cost Basis of Collateral	7,113,471,000
Carrying Value of Collateral	7,786,425,000
Residential Mortgage | Repurchase Agreements
Debt Instrument [Line Items]
Outstanding Face Amount	5,165,150,000
Carrying Value	$ 5,164,159,000	3,678,246,000
Weighted Average Funding Cost	3.74%
Weighted Average Life (Years)	18 days
Residential Mortgage | Repurchase Agreements | Collateral
Debt Instrument [Line Items]
Weighted Average Life (Years)	13 years 10 months 24 days
Outstanding Face of Collateral	$ 5,960,958,000
Amortized Cost Basis of Collateral	6,025,596,000
Carrying Value of Collateral	5,805,242,000
Residential Mortgage | Notes and Bonds Payable
Debt Instrument [Line Items]
Outstanding Face Amount	1,012,342,000
Carrying Value	$ 1,015,360,000	124,945,000
Weighted Average Funding Cost	4.09%
Weighted Average Life (Years)	3 years 8 months 12 days
Residential Mortgage | Notes and Bonds Payable | Collateral
Debt Instrument [Line Items]
Weighted Average Life (Years)	8 years
Outstanding Face of Collateral	$ 1,258,875,000
Amortized Cost Basis of Collateral	1,277,193,000
Carrying Value of Collateral	1,194,186,000
Real Estate Owned | Repurchase Agreements
Debt Instrument [Line Items]
Outstanding Face Amount	68,651,000
Carrying Value	$ 68,635,000	94,868,000
Weighted Average Funding Cost	3.85%
Weighted Average Life (Years)	12 days
Real Estate Owned | Repurchase Agreements | Collateral
Debt Instrument [Line Items]
Carrying Value of Collateral	$ 95,410,000
Total Repurchase Agreements | Repurchase Agreements
Debt Instrument [Line Items]
Outstanding Face Amount	23,111,366,000
Carrying Value	$ 23,110,359,000	15,553,969,000
Weighted Average Funding Cost	2.87%
Weighted Average Life (Years)	9 days
MSR purchase price holdback	$ 77,800,000
Excess MSRs
Debt Instrument [Line Items]
Carrying Value	269,759,000	297,563,000
Excess MSRs | Notes and Bonds Payable
Debt Instrument [Line Items]
Outstanding Face Amount	269,759,000
Carrying Value	$ 269,759,000	297,563,000
Weighted Average Funding Cost	4.95%
Weighted Average Life (Years)	1 year 10 months 24 days
Excess MSRs | Notes and Bonds Payable | Collateral
Debt Instrument [Line Items]
Weighted Average Life (Years)	5 years 9 months 18 days
Outstanding Face of Collateral	$ 103,514,484,000
Amortized Cost Basis of Collateral	315,847,000
Carrying Value of Collateral	416,899,000
MSRs | Notes and Bonds Payable
Debt Instrument [Line Items]
Outstanding Face Amount	2,360,182,000
Carrying Value	$ 2,352,961,000	2,360,856,000
Weighted Average Funding Cost	4.23%
Weighted Average Life (Years)	2 years
MSRs | Notes and Bonds Payable | Collateral
Debt Instrument [Line Items]
Weighted Average Life (Years)	5 years 6 months
Outstanding Face of Collateral	$ 452,215,330,000
Amortized Cost Basis of Collateral	4,718,333,000
Carrying Value of Collateral	5,113,271,000
Servicer Advances
Debt Instrument [Line Items]
Carrying Value	2,896,819,000	3,382,455,000
Servicer Advances | Notes and Bonds Payable
Debt Instrument [Line Items]
Outstanding Face Amount	2,903,093,000
Carrying Value	$ 2,896,819,000	3,382,455,000
Weighted Average Funding Cost	3.22%
Weighted Average Life (Years)	2 years
Face amount of debt at fixed rate	$ 2,600,000,000
Servicer Advances | Notes and Bonds Payable | London Interbank Offered Rate (LIBOR) | Minimum
Debt Instrument [Line Items]
Variable interest rate spread	1.15%
Servicer Advances | Notes and Bonds Payable | London Interbank Offered Rate (LIBOR) | Maximum
Debt Instrument [Line Items]
Variable interest rate spread	1.99%
Servicer Advances | Notes and Bonds Payable | Collateral
Debt Instrument [Line Items]
Weighted Average Life (Years)	1 year 7 months 6 days
Outstanding Face of Collateral	$ 3,316,416,000
Amortized Cost Basis of Collateral	3,482,368,000
Carrying Value of Collateral	3,512,345,000
Consumer Loans
Debt Instrument [Line Items]
Carrying Value	870,973,000	936,447,000
Consumer Loans | Notes and Bonds Payable
Debt Instrument [Line Items]
Outstanding Face Amount	868,214,000
Carrying Value	$ 870,973,000	936,447,000
Weighted Average Funding Cost	3.25%
Weighted Average Life (Years)	4 years
Consumer Loans | Notes and Bonds Payable | Collateral
Debt Instrument [Line Items]
Weighted Average Life (Years)	5 years 7 months 6 days
Outstanding Face of Collateral	$ 878,317,000
Amortized Cost Basis of Collateral	884,473,000
Carrying Value of Collateral	881,069,000
Total Notes Payable | Notes and Bonds Payable
Debt Instrument [Line Items]
Outstanding Face Amount	7,413,590,000
Carrying Value	$ 7,405,872,000	$ 7,102,266,000
Weighted Average Funding Cost	3.73%
Weighted Average Life (Years)	2 years 6 months
Non-agency RMBS Repurchase Agreements, LIBOR Based Floating Interest Rate | Repurchase Agreements
Debt Instrument [Line Items]
Outstanding Face Amount	$ 6,585,600,000
Non-agency RMBS Repurchase Agreements, Fixed Rate | Repurchase Agreements
Debt Instrument [Line Items]
Outstanding Face Amount	558,800,000
Corporate Note, LIBOR Based Floating Interest Rate | Secured Debt
Debt Instrument [Line Items]
Outstanding Face Amount	169,800,000
3.00% Secured Corporate Note | Secured Debt
Debt Instrument [Line Items]
Outstanding Face Amount	$ 100,000,000.0
3.00% Secured Corporate Note | Secured Debt | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Variable interest rate spread	3.00%
2.50% Secured Corporate Note | Secured Debt | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Variable interest rate spread	2.50%
2.25% Agency MSR Secured Note | Secured Debt
Debt Instrument [Line Items]
Outstanding Face Amount	$ 940,200,000
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	2.75%
3.55% Corporate Note | Secured Debt
Debt Instrument [Line Items]
Outstanding Face Amount	$ 1,419,900,000
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 and Bonds Payable | Nationstar
Debt Instrument [Line Items]
Outstanding Face Amount	$ 6,000,000.0
Collateral amount	$ 1,500,000
2.88% Residential Mortgage Loans | Notes and Bonds Payable | London Interbank Offered Rate (LIBOR) | Nationstar
Debt Instrument [Line Items]
Variable interest rate spread	2.88%
Non-Agency RMBS | Notes and Bonds Payable
Debt Instrument [Line Items]
Outstanding Face Amount	$ 109,900,000
Non-Agency RMBS | Notes and Bonds Payable | Minimum
Debt Instrument [Line Items]
Weighted Average Funding Cost	3.50%
Non-Agency RMBS | Notes and Bonds Payable | Maximum
Debt Instrument [Line Items]
Weighted Average Funding Cost	3.76%
4.59% Asset-backed Notes | Secured Debt
Debt Instrument [Line Items]
Outstanding Face Amount	$ 362,100,000
Weighted Average Funding Cost	4.59%
Asset-backed Notes, LIBOR Based Floating Interest Rate | Secured Debt
Debt Instrument [Line Items]
Outstanding Face Amount	$ 535,100,000
Collateral amount	$ 1,300,000
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]
UPB of Underlying Mortgages	$ 787,900,000
Interest rate, stated percentage	3.20%
Consumer Loan, UPB Class B | Secured Debt
Debt Instrument [Line Items]
UPB of Underlying Mortgages	$ 70,400,000
Interest rate, stated percentage	3.58%
Consumer Loan, UPB Class C-1 | Secured Debt
Debt Instrument [Line Items]
UPB of Underlying Mortgages	$ 8,700,000
Interest rate, stated percentage	5.06%
4.00% Consumer Loans | Secured Debt
Debt Instrument [Line Items]
Outstanding Face Amount	$ 1,200,000
Interest rate, stated percentage	4.00%