MORTGAGE SERVICING RIGHTS AND MSR FINANCING RECEIVABLES - Summary of the Geographic Distribution of the Underlying Residential Mortgage Loans of the MSRs (Details) - MSRs - Mortgage Loans	Dec. 31, 2021	Dec. 31, 2020
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	18.10%	21.20%
Florida
Schedule of MSRs [Line Items]
Percentage of Total Outstanding Unpaid Principal Amount	8.60%	7.40%
Texas
Schedule of MSRs [Line Items]
Percentage of Total Outstanding Unpaid Principal Amount	6.20%	5.60%
New York
Schedule of MSRs [Line Items]
Percentage of Total Outstanding Unpaid Principal Amount	6.00%	7.00%
Washington
Schedule of MSRs [Line Items]
Percentage of Total Outstanding Unpaid Principal Amount	5.60%	2.90%
New Jersey
Schedule of MSRs [Line Items]
Percentage of Total Outstanding Unpaid Principal Amount	4.50%	4.80%
Virginia
Schedule of MSRs [Line Items]
Percentage of Total Outstanding Unpaid Principal Amount	3.40%	2.90%
Illinois
Schedule of MSRs [Line Items]
Percentage of Total Outstanding Unpaid Principal Amount	3.40%	3.60%
Maryland
Schedule of MSRs [Line Items]
Percentage of Total Outstanding Unpaid Principal Amount	3.40%	3.10%
Georgia
Schedule of MSRs [Line Items]
Percentage of Total Outstanding Unpaid Principal Amount	3.00%	3.30%
Other U.S.
Schedule of MSRs [Line Items]
Percentage of Total Outstanding Unpaid Principal Amount	37.80%	38.20%