REAL ESTATE SECURITIES - Summary of Securities (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) securities	Dec. 31, 2014 USD ($) securities
Schedule of Available-for-sale Securities [Line Items]
Outstanding Face Amount	$ 10,084,386	$ 10,950,979
Amortized Cost Basis	2,415,727	2,786,317
Gross Unrealized Gains	6,936	33,222
Gross Unrealized Losses	(15,446)	(3,973)
Carrying Value	$ 2,407,217	$ 2,815,566
Number of Securities | securities	200	235
Weighted Average Coupon %	1.44%	1.50%
Weighted Average Yield %	3.60%	4.54%
Remaining Duration (years)	3 years 3 months 14 days	4 years 1 month 24 days
CMBS
Schedule of Available-for-sale Securities [Line Items]
Outstanding Face Amount	$ 1,972,492	$ 2,247,565
Amortized Cost Basis	1,994,928	2,277,995
Gross Unrealized Gains	4,643	28,453
Gross Unrealized Losses	(8,065)	(1,038)
Carrying Value	$ 1,991,506	$ 2,305,410
Number of Securities | securities	119	145
Weighted Average Coupon %	3.17%	3.31%
Weighted Average Yield %	2.59%	2.60%
Remaining Duration (years)	3 years 1 month 24 days	4 years 2 months 23 days
CMBS interest-only
Schedule of Available-for-sale Securities [Line Items]
Outstanding Face Amount	$ 7,436,379	$ 7,239,503
Amortized Cost Basis	348,222	376,085
Gross Unrealized Gains	1,027	2,973
Gross Unrealized Losses	(4,826)	(723)
Carrying Value	$ 344,423	$ 378,335
Number of Securities | securities	48	41
Weighted Average Coupon %	1.02%	1.04%
Weighted Average Yield %	3.81%	4.88%
Remaining Duration (years)	3 years 4 months 2 days	3 years 5 months 12 days
GNMA interest-only
Schedule of Available-for-sale Securities [Line Items]
Outstanding Face Amount	$ 632,175	$ 1,400,141
Amortized Cost Basis	28,311	67,544
Gross Unrealized Gains	44	1,035
Gross Unrealized Losses	(2,161)	(1,937)
Carrying Value	$ 26,194	$ 66,642
Number of Securities | securities	20	34
Weighted Average Coupon %	0.80%	0.85%
Weighted Average Yield %	4.26%	5.90%
Remaining Duration (years)	5 years 2 months 19 days	4 years 6 months
GN construction securities
Schedule of Available-for-sale Securities [Line Items]
Outstanding Face Amount	$ 27,091	$ 27,538
Amortized Cost Basis	27,581	28,178
Gross Unrealized Gains	1,058	503
Gross Unrealized Losses	0	(275)
Carrying Value	$ 28,639	$ 28,406
Number of Securities | securities	1	4
Weighted Average Coupon %	4.10%	3.89%
Weighted Average Yield %	3.86%	3.56%
Remaining Duration (years)	9 years 3 months 29 days	9 years 5 months 1 day
GN permanent securities
Schedule of Available-for-sale Securities [Line Items]
Outstanding Face Amount	$ 16,249	$ 36,232
Amortized Cost Basis	16,685	36,515
Gross Unrealized Gains	164	258
Gross Unrealized Losses	(394)	0
Carrying Value	$ 16,455	$ 36,773
Number of Securities | securities	12	11
Weighted Average Coupon %	4.52%	5.49%
Weighted Average Yield %	3.94%	4.94%
Remaining Duration (years)	5 years 5 months 4 days	1 year 3 months 25 days