EXCESS MORTGAGE SERVICING RIGHTS ASSETS - Summary of Direct Investments in Excess MSRs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Schedule of Equity Method Investments [Line Items]
Weighted Average Life (Years)	1 year 6 months
Carrying Value	$ 5,045,339		$ 4,585,841
Servicer advance investments | Servicer Advance Investments
Schedule of Equity Method Investments [Line Items]
UPB of Underlying Mortgages	24,439,045		26,061,499
Original and Recaptured Pools
Schedule of Equity Method Investments [Line Items]
Original and Recaptured Pools	(4,618)	$ (11,024)
Excess MSRs
Schedule of Equity Method Investments [Line Items]
UPB of Underlying Mortgages	$ 68,367,358
Weighted Average Life (Years)	6 years 4 months 24 days
Servicing Asset at Amortized Cost	$ 248,147
Carrying Value	303,568		310,938
Excess MSRs | Mr. Cooper
Schedule of Equity Method Investments [Line Items]
Carrying Value	$ 301,849		309,009
Excess MSRs | Agency
Schedule of Equity Method Investments [Line Items]
Weighted Average Life (Years)	6 years 1 month 6 days
Excess MSRs | Agency | Original and Recaptured Pools
Schedule of Equity Method Investments [Line Items]
UPB of Underlying Mortgages	$ 32,373,398
Servicing Asset at Amortized Cost	139,870
Carrying Value	$ 157,633		162,645
Excess MSRs | Agency | Original and Recaptured Pools | Minimum
Schedule of Equity Method Investments [Line Items]
Interest in Excess MSR	32.50%
Excess MSRs | Agency | Original and Recaptured Pools | Maximum
Schedule of Equity Method Investments [Line Items]
Interest in Excess MSR	66.70%
Excess MSRs | Agency | Original and Recaptured Pools | Weighted Average
Schedule of Equity Method Investments [Line Items]
Interest in Excess MSR	53.30%
Excess MSRs | Agency | Fortress-managed funds | Original and Recaptured Pools | Minimum
Schedule of Equity Method Investments [Line Items]
Interest in Excess MSR	0.00%
Excess MSRs | Agency | Fortress-managed funds | Original and Recaptured Pools | Maximum
Schedule of Equity Method Investments [Line Items]
Interest in Excess MSR	40.00%
Excess MSRs | Agency | Mr. Cooper | Original and Recaptured Pools | Minimum
Schedule of Equity Method Investments [Line Items]
Interest in Excess MSR	20.00%
Excess MSRs | Agency | Mr. Cooper | Original and Recaptured Pools | Maximum
Schedule of Equity Method Investments [Line Items]
Interest in Excess MSR	35.00%
Excess MSRs | Non-Agency
Schedule of Equity Method Investments [Line Items]
Weighted Average Life (Years)	6 years 8 months 12 days
Excess MSRs | Non-Agency | Original and Recaptured Pools
Schedule of Equity Method Investments [Line Items]
UPB of Underlying Mortgages	$ 35,993,960
Servicing Asset at Amortized Cost	108,277
Carrying Value	$ 145,935		$ 148,293
Excess MSRs | Non-Agency | Original and Recaptured Pools | Minimum
Schedule of Equity Method Investments [Line Items]
Interest in Excess MSR	33.30%
Excess MSRs | Non-Agency | Original and Recaptured Pools | Maximum
Schedule of Equity Method Investments [Line Items]
Interest in Excess MSR	100.00%
Excess MSRs | Non-Agency | Original and Recaptured Pools | Weighted Average
Schedule of Equity Method Investments [Line Items]
Interest in Excess MSR	59.40%
Excess MSRs | Non-Agency | Fortress-managed funds | Original and Recaptured Pools | Minimum
Schedule of Equity Method Investments [Line Items]
Interest in Excess MSR	0.00%
Excess MSRs | Non-Agency | Fortress-managed funds | Original and Recaptured Pools | Maximum
Schedule of Equity Method Investments [Line Items]
Interest in Excess MSR	50.00%
Excess MSRs | Non-Agency | Mr. Cooper | Original and Recaptured Pools | Minimum
Schedule of Equity Method Investments [Line Items]
Interest in Excess MSR	0.00%
Excess MSRs | Non-Agency | Mr. Cooper | Original and Recaptured Pools | Maximum
Schedule of Equity Method Investments [Line Items]
Interest in Excess MSR	33.30%