LOANS - Additional Information about Residential Mortgage Loans (Details) - Residential Mortgage Loans $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) point	Dec. 31, 2018 USD ($) point	Dec. 31, 2017 USD ($) point
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Unpaid principal balance	$ 4,133,149	$ 2,425,657
Minimum
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Unpaid principal balance		$ 1	$ 0
Interest rate		2.00%	2.00%
FICO score at loan origination | point		505	505
Loan-to-value ratio at loan origination		8.00%	8.00%
Maximum
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Unpaid principal balance		$ 3,448	$ 3,500
Interest rate		8.38%	7.75%
FICO score at loan origination | point		829	823
Loan-to-value ratio at loan origination		105.00%	111.00%
Weighted Average
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Unpaid principal balance	$ 459	$ 457
Interest rate	4.94%	4.72%
FICO score at loan origination | point	758	752
Loan-to-value ratio at loan origination	67.00%	68.00%