Quarterly report pursuant to Section 13 or 15(d)

INVESTMENTS IN EXCESS MORTGAGE SERVICING RIGHTS - Summary of Direct Investments in Excess MSRs (Details)

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INVESTMENTS IN EXCESS MORTGAGE SERVICING RIGHTS - Summary of Direct Investments in Excess MSRs (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Dec. 31, 2017
Investment [Line Items]          
UPB of Underlying Mortgages $ 84,100,000   $ 84,100,000    
Weighted Average Life (Years)     1 year 8 days    
Principal investment gain (loss) (4,744) $ (14,291) $ (55,711) $ (32,650)  
Servicer Advance Investments | Servicer Advances          
Investment [Line Items]          
UPB of Underlying Mortgages 42,323,957   42,323,957   $ 139,460,371
Original and Recaptured Pools          
Investment [Line Items]          
Principal investment gain (loss) (851) (12,047) (46,540) (41,032)  
Recapture Agreements          
Investment [Line Items]          
Principal investment gain (loss) (3,893) $ (2,244) (9,171) $ 8,382  
Excess MSRs          
Investment [Line Items]          
UPB of Underlying Mortgages 112,054,333   $ 112,054,333    
Weighted Average Life (Years)     6 years 1 month 6 days    
Amortized Cost Basis 377,583   $ 377,583    
Carrying Value 467,061   467,061   1,173,713
Excess MSRs | Nationstar          
Investment [Line Items]          
Carrying Value 464,503   464,503   532,233
Excess MSRs | Agency          
Investment [Line Items]          
UPB of Underlying Mortgages 55,677,339   $ 55,677,339    
Weighted Average Life (Years)     6 years 1 month 6 days    
Amortized Cost Basis 231,902   $ 231,902    
Carrying Value 273,853   273,853   324,636
Excess MSRs | Agency | Original and Recaptured Pools          
Investment [Line Items]          
UPB of Underlying Mortgages 55,677,339   $ 55,677,339    
Weighted Average Life (Years)     5 years 7 months 6 days    
Amortized Cost Basis 215,972   $ 215,972    
Carrying Value $ 242,655   $ 242,655   280,033
Excess MSRs | Agency | Original and Recaptured Pools | Minimum          
Investment [Line Items]          
Interest in Excess MSR 32.50%   32.50%    
Excess MSRs | Agency | Original and Recaptured Pools | Maximum          
Investment [Line Items]          
Interest in Excess MSR 66.70%   66.70%    
Excess MSRs | Agency | Original and Recaptured Pools | Weighted Average          
Investment [Line Items]          
Interest in Excess MSR 53.30%   53.30%    
Excess MSRs | Agency | Recapture Agreements          
Investment [Line Items]          
UPB of Underlying Mortgages $ 0   $ 0    
Weighted Average Life (Years)     12 years 10 months 24 days    
Amortized Cost Basis 15,930   $ 15,930    
Carrying Value $ 31,198   $ 31,198   44,603
Excess MSRs | Agency | Recapture Agreements | Minimum          
Investment [Line Items]          
Interest in Excess MSR 32.50%   32.50%    
Excess MSRs | Agency | Recapture Agreements | Maximum          
Investment [Line Items]          
Interest in Excess MSR 66.70%   66.70%    
Excess MSRs | Agency | Recapture Agreements | Weighted Average          
Investment [Line Items]          
Interest in Excess MSR 53.30%   53.30%    
Excess MSRs | Agency | Fortress-managed funds | Original and Recaptured Pools | Minimum          
Investment [Line Items]          
Interest in Excess MSR 0.00%   0.00%    
Excess MSRs | Agency | Fortress-managed funds | Original and Recaptured Pools | Maximum          
Investment [Line Items]          
Interest in Excess MSR 40.00%   40.00%    
Excess MSRs | Agency | Fortress-managed funds | Recapture Agreements | Minimum          
Investment [Line Items]          
Interest in Excess MSR 0.00%   0.00%    
Excess MSRs | Agency | Fortress-managed funds | Recapture Agreements | Maximum          
Investment [Line Items]          
Interest in Excess MSR 40.00%   40.00%    
Excess MSRs | Agency | Nationstar | Original and Recaptured Pools | Minimum          
Investment [Line Items]          
Interest in Excess MSR 20.00%   20.00%    
Excess MSRs | Agency | Nationstar | Original and Recaptured Pools | Maximum          
Investment [Line Items]          
Interest in Excess MSR 35.00%   35.00%    
Excess MSRs | Agency | Nationstar | Recapture Agreements | Minimum          
Investment [Line Items]          
Interest in Excess MSR 20.00%   20.00%    
Excess MSRs | Agency | Nationstar | Recapture Agreements | Maximum          
Investment [Line Items]          
Interest in Excess MSR 35.00%   35.00%    
Excess MSRs | Non-Agency          
Investment [Line Items]          
UPB of Underlying Mortgages $ 56,376,994   $ 56,376,994    
Weighted Average Life (Years)     6 years    
Amortized Cost Basis 145,681   $ 145,681    
Carrying Value 193,208   193,208   849,077
Excess MSRs | Non-Agency | Original and Recaptured Pools          
Investment [Line Items]          
UPB of Underlying Mortgages 56,376,994   $ 56,376,994    
Weighted Average Life (Years)     5 years 9 months 18 days    
Amortized Cost Basis 140,698   $ 140,698    
Carrying Value $ 174,680   $ 174,680   190,696
Excess MSRs | Non-Agency | Original and Recaptured Pools | Minimum          
Investment [Line Items]          
Interest in Excess MSR 33.30%   33.30%    
Excess MSRs | Non-Agency | Original and Recaptured Pools | Maximum          
Investment [Line Items]          
Interest in Excess MSR 100.00%   100.00%    
Excess MSRs | Non-Agency | Original and Recaptured Pools | Weighted Average          
Investment [Line Items]          
Interest in Excess MSR 59.40%   59.40%    
Excess MSRs | Non-Agency | Recapture Agreements          
Investment [Line Items]          
UPB of Underlying Mortgages $ 0   $ 0    
Weighted Average Life (Years)     12 years 8 months 12 days    
Amortized Cost Basis 4,983   $ 4,983    
Carrying Value $ 18,528   $ 18,528   19,814
Excess MSRs | Non-Agency | Recapture Agreements | Minimum          
Investment [Line Items]          
Interest in Excess MSR 33.30%   33.30%    
Excess MSRs | Non-Agency | Recapture Agreements | Maximum          
Investment [Line Items]          
Interest in Excess MSR 100.00%   100.00%    
Excess MSRs | Non-Agency | Recapture Agreements | Weighted Average          
Investment [Line Items]          
Interest in Excess MSR 59.40%   59.40%    
Excess MSRs | Non-Agency | Ocwen Serviced Pools          
Investment [Line Items]          
UPB of Underlying Mortgages $ 0   $ 0    
Interest in Excess MSR 0.00%   0.00%    
Weighted Average Life (Years)     0 years    
Amortized Cost Basis $ 0   $ 0    
Carrying Value $ 0   $ 0   $ 638,567
Excess MSRs | Non-Agency | Fortress-managed funds | Original and Recaptured Pools | Minimum          
Investment [Line Items]          
Interest in Excess MSR 0.00%   0.00%    
Excess MSRs | Non-Agency | Fortress-managed funds | Original and Recaptured Pools | Maximum          
Investment [Line Items]          
Interest in Excess MSR 50.00%   50.00%    
Excess MSRs | Non-Agency | Fortress-managed funds | Recapture Agreements | Minimum          
Investment [Line Items]          
Interest in Excess MSR 0.00%   0.00%    
Excess MSRs | Non-Agency | Fortress-managed funds | Recapture Agreements | Maximum          
Investment [Line Items]          
Interest in Excess MSR 50.00%   50.00%    
Excess MSRs | Non-Agency | Fortress-managed funds | Ocwen Serviced Pools          
Investment [Line Items]          
Interest in Excess MSR 0.00%   0.00%    
Excess MSRs | Non-Agency | Nationstar | Original and Recaptured Pools | Minimum          
Investment [Line Items]          
Interest in Excess MSR 0.00%   0.00%    
Excess MSRs | Non-Agency | Nationstar | Original and Recaptured Pools | Maximum          
Investment [Line Items]          
Interest in Excess MSR 33.30%   33.30%    
Excess MSRs | Non-Agency | Nationstar | Recapture Agreements | Minimum          
Investment [Line Items]          
Interest in Excess MSR 0.00%   0.00%    
Excess MSRs | Non-Agency | Nationstar | Recapture Agreements | Maximum          
Investment [Line Items]          
Interest in Excess MSR 33.30%   33.30%    
Excess MSRs | Non-Agency | Nationstar | Ocwen Serviced Pools          
Investment [Line Items]          
Interest in Excess MSR 0.00%   0.00%