LOANS - Geographic Concentrations Based on Unpaid Principal Balances (Details) - Residential mortgage loans - Geographic Concentration Risk	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
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	52.10%	53.70%
New York
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Geographic concentrations of residential mortgage loans	10.50%	6.60%
Florida
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Geographic concentrations of residential mortgage loans	5.30%	7.10%
Other
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Geographic concentrations of residential mortgage loans	32.10%	32.60%