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LOANS - Geographic Concentrations Based on Unpaid Principal Balances (Details) - Residential mortgage loans - Geographic Concentration Risk | 3 Months Ended | 12 Months Ended
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Mar. 31, 2021 | Dec. 31, 2020
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |
Geographic Concentrations of Residential Mortgage Loans | 100.00% | 100.00%
California |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |
Geographic Concentrations of Residential Mortgage Loans | 51.00% | 48.90%
New York |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |
Geographic Concentrations of Residential Mortgage Loans | 14.00% | 14.00%
Florida |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |
Geographic Concentrations of Residential Mortgage Loans | 6.00% | 6.00%
All other (none individually greater than 5%) |  |
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] |  |
Geographic Concentrations of Residential Mortgage Loans | 29.00% | 31.10%

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