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LOANS - Geographic Concentrations Based on Unpaid Principal Balances (Details) - Residential mortgage loans - Geographic Concentration Risk | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019
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 | 48.90% | 52.10%
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% | 10.50%
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% | 5.30%
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 | 31.10% | 32.10%

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