LOANS - Additional Information about Residential Mortgage Loans (Details) - Residential Mortgage $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019 USD ($) point	Dec. 31, 2018 USD ($) point
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Unpaid principal balance	$ 3,076,415	$ 2,425,657
Minimum
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Unpaid principal balance	$ 0	$ 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	9.25%	7.75%
FICO score at loan origination | point	823	823
Loan-to-value ratio at loan origination	116.00%	111.00%
Weighted Average
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Unpaid principal balance	$ 455	$ 457
Interest rate	5.07%	4.72%
FICO score at loan origination | point	753	752
Loan-to-value ratio at loan origination	67.00%	68.00%