FAIR VALUE OF FINANCIAL INSTRUMENTS - Schedule of Quantitative Information (Details) - Discounted Cash Flow - Level 3 - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Carrying Value	$ 1,701,980	$ 2,100,947
CMBS
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Carrying Value	$ 1,325,250	$ 1,701,395
CMBS | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)	1.41%	1.35%
Duration (in years)	3 days	0 days
CMBS | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)	2.79%	2.87%
Duration (in years)	3 years 7 months 24 days	3 years 6 months 18 days
CMBS | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)	8.62%	9.18%
Duration (in years)	7 years 11 months 26 days	9 years 3 days
CMBS interest-only
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Carrying Value	$ 320,865	$ 342,171
CMBS interest-only | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)	2.62%	2.84%
Duration (in years)	22 days	0 years
Prepayment speed	100.00	100.00
CMBS interest-only | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)	3.52%	4.04%
Duration (in years)	3 years 10 days	2 years 11 months 26 days
Prepayment speed	100.00	100.00
CMBS interest-only | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)	4.24%	4.80%
Duration (in years)	4 years 2 months 19 days	4 years 4 months 13 days
Prepayment speed	100.00	100.00
GNMA interest-only
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Carrying Value	$ 15,625	$ 16,821
GNMA interest-only | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)	3.84%	0.87%
Duration (in years)	7 days	1 year 8 months 8 days
Prepayment speed	5.00	5.00
GNMA interest-only | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)	8.28%	7.22%
Duration (in years)	2 years 4 months 6 days	4 years 5 months 8 days
Prepayment speed	13.33	13.80
GNMA interest-only | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)	50.65%	48.64%
Duration (in years)	5 years 2 months 15 days	20 years 7 months 28 days
Prepayment speed	35.00	35.00
Agency securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Carrying Value	$ 771	$ 780
Agency securities | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)	1.40%	1.40%
Duration (in years)	0 months	2 years 7 months 9 days
Agency securities | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)	2.06%	2.17%
Duration (in years)	3 years 5 months 19 days	3 years 3 months 7 days
Agency securities | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)	2.43%	2.63%
Duration (in years)	5 years 4 months 17 days	4 years 4 months 20 days
GNMA permanent securities
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Carrying Value	$ 39,469	$ 39,780
GNMA permanent securities | Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)	2.73%	2.63%
Duration (in years)	1 year 8 months 26 days	1 year 11 months 1 day
GNMA permanent securities | Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)	3.63%	3.65%
Duration (in years)	6 years 1 month 13 days	10 years 3 months 18 days
GNMA permanent securities | Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Yield (as a percent)	6.37%	6.92%
Duration (in years)	6 years 5 months 19 days	15 years 7 months 28 days