REAL ESTATE SECURITIES - Securities by Remaining Maturity (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Within 1 year	$ 604,328		$ 604,328		$ 502,019
1-5 years	1,151,625		1,151,625		1,237,641
5-10 years	658,868		658,868		1,053,190
After 10 years	561		561		22,716
Fair value of real estate securities	2,415,382		2,415,382		2,815,566
Other than temporary impairments included in consolidated statements of income	(200)	$ (500)	(1,600)	$ (2,100)
CMBS
Schedule of Available-for-sale Securities [Line Items]
Within 1 year	604,249		604,249		474,357
1-5 years	776,565		776,565		814,702
5-10 years	604,381		604,381		1,016,351
After 10 years	0		0		0
Fair value of real estate securities	1,985,195		1,985,195		2,305,410
CMBS interest-only
Schedule of Available-for-sale Securities [Line Items]
Within 1 year	70		70		391
1-5 years	356,858		356,858		370,993
5-10 years	0		0		6,951
After 10 years	0		0		0
Fair value of real estate securities	356,928		356,928		378,335
GNMA interest-only
Schedule of Available-for-sale Securities [Line Items]
Within 1 year	9		9		1,356
1-5 years	8,929		8,929		42,105
5-10 years	19,104		19,104		23,181
After 10 years	561		561		0
Fair value of real estate securities	28,603		28,603		66,642
GN construction securities
Schedule of Available-for-sale Securities [Line Items]
Within 1 year	0		0		0
1-5 years	414		414		507
5-10 years	27,435		27,435		5,183
After 10 years	0		0		22,716
Fair value of real estate securities	27,849		27,849		28,406
GN permanent securities
Schedule of Available-for-sale Securities [Line Items]
Within 1 year	0		0		25,915
1-5 years	8,859		8,859		9,334
5-10 years	7,948		7,948		1,524
After 10 years	0		0		0
Fair value of real estate securities	$ 16,807		$ 16,807		$ 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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