FAIR VALUE MEASUREMENT - Schedule of Inputs Used in Valuing Residential Mortgage Loans (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted Average Life (Years)	1 year 4 months 30 days
Performing Loans
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Weighted Average Life (Years)	5 years 3 months 22 days
Fair Value, Measurements, Nonrecurring
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount Rate	4.00%
Weighted Average Life (Years)	4 years 11 months 2 days
Prepayment Rate	8.90%
CDR	1.30%
Loss Severity	36.60%
Fair Value, Measurements, Nonrecurring | Performing Loans
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount Rate	4.00%
Weighted Average Life (Years)	5 years 1 month 14 days
Prepayment Rate	10.30%
CDR	1.50%
Loss Severity	31.60%
Fair Value, Measurements, Nonrecurring | Non-Performing Loans
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount Rate	6.60%
Weighted Average Life (Years)	3 years 2 months 8 days
Prepayment Rate	3.00%
CDR	3.00%
Loss Severity	30.00%
Fair Value, Measurements, Nonrecurring | Fair Value
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 265,243
Fair Value, Measurements, Nonrecurring | Fair Value | Performing Loans
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	215,406
Fair Value, Measurements, Nonrecurring | Fair Value | Non-Performing Loans
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair Value	$ 49,837