REAL ESTATE SECURITIES - Securities by Remaining Maturity (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Within 1 year	$ 612,752	$ 502,019
1-5 years	1,260,381	1,237,641
5-10 years	533,604	1,053,190
After 10 years	480	22,716
Fair value of real estate securities	2,407,217	2,815,566
Other than temporary impairments included in consolidated statements of income	(1,600)	(3,900)	$ (2,500)
CMBS
Schedule of Available-for-sale Securities [Line Items]
Within 1 year	610,526	474,357
1-5 years	891,752	814,702
5-10 years	489,228	1,016,351
After 10 years	0	0
Fair value of real estate securities	1,991,506	2,305,410
CMBS interest-only
Schedule of Available-for-sale Securities [Line Items]
Within 1 year	0	391
1-5 years	344,423	370,993
5-10 years	0	6,951
After 10 years	0	0
Fair value of real estate securities	344,423	378,335
GNMA interest-only
Schedule of Available-for-sale Securities [Line Items]
Within 1 year	6	1,356
1-5 years	17,159	42,105
5-10 years	8,549	23,181
After 10 years	480	0
Fair value of real estate securities	26,194	66,642
GN construction securities
Schedule of Available-for-sale Securities [Line Items]
Within 1 year	0	0
1-5 years	386	507
5-10 years	28,253	5,183
After 10 years	0	22,716
Fair value of real estate securities	28,639	28,406
GN permanent securities
Schedule of Available-for-sale Securities [Line Items]
Within 1 year	2,220	25,915
1-5 years	6,661	9,334
5-10 years	7,574	1,524
After 10 years	0	0
Fair value of real estate securities	$ 16,455	$ 36,773

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49167202&loc=d3e26610-111562

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

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