Quarterly report pursuant to Section 13 or 15(d)

INVESTMENTS IN MORTGAGE SERVICING RIGHTS AND MORTGAGE SERVICING RIGHTS FINANCING RECEIVABLES - Summary of the Geographic Distribution of the Underlying Residential Mortgage Loans (Details)

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INVESTMENTS IN MORTGAGE SERVICING RIGHTS AND MORTGAGE SERVICING RIGHTS FINANCING RECEIVABLES - Summary of the Geographic Distribution of the Underlying Residential Mortgage Loans (Details) - MSRs - Mortgage Loans
Sep. 30, 2018
Dec. 31, 2017
Schedule of MSRs [Line Items]    
Percentage of Total Outstanding Unpaid Principal Amount 100.00% 100.00%
California    
Schedule of MSRs [Line Items]    
Percentage of Total Outstanding Unpaid Principal Amount 20.50% 19.00%
New York    
Schedule of MSRs [Line Items]    
Percentage of Total Outstanding Unpaid Principal Amount 8.10% 6.30%
Florida    
Schedule of MSRs [Line Items]    
Percentage of Total Outstanding Unpaid Principal Amount 7.00% 6.00%
Texas    
Schedule of MSRs [Line Items]    
Percentage of Total Outstanding Unpaid Principal Amount 5.20% 5.70%
New Jersey    
Schedule of MSRs [Line Items]    
Percentage of Total Outstanding Unpaid Principal Amount 5.10% 5.20%
Illinois    
Schedule of MSRs [Line Items]    
Percentage of Total Outstanding Unpaid Principal Amount 3.90% 4.10%
Massachusetts    
Schedule of MSRs [Line Items]    
Percentage of Total Outstanding Unpaid Principal Amount 3.60% 3.80%
Maryland    
Schedule of MSRs [Line Items]    
Percentage of Total Outstanding Unpaid Principal Amount 3.40% 2.80%
Pennsylvania    
Schedule of MSRs [Line Items]    
Percentage of Total Outstanding Unpaid Principal Amount 3.20% 3.30%
Virginia    
Schedule of MSRs [Line Items]    
Percentage of Total Outstanding Unpaid Principal Amount 3.20% 3.10%
Other U.S.    
Schedule of MSRs [Line Items]    
Percentage of Total Outstanding Unpaid Principal Amount 36.80% 40.70%