LOANS - Geographic Concentrations Based on Unpaid Principal Balances (Details) - Residential mortgage loans - Geographic Concentration Risk	12 Months Ended
	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%