REAL ESTATE SECURITIES - Securities by Remaining Maturity (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Within 1 year	$ 77,782		$ 143,918
1-5 years	1,345,965		1,508,191
5-10 years	278,184		441,038
After 10 years	49		7,800
Fair value of real estate securities	1,701,980		2,100,947
Other than temporary impairment losses included in consolidated statements of income	400	$ 600
CMBS
Schedule of Available-for-sale Securities [Line Items]
Within 1 year	74,889		132,730
1-5 years	1,008,680		1,156,026
5-10 years	241,681		412,639
After 10 years	0		0
Fair value of real estate securities	1,325,250		1,701,395
CMBS interest-only
Schedule of Available-for-sale Securities [Line Items]
Within 1 year	1,128		11,188
1-5 years	319,737		330,983
5-10 years	0		0
After 10 years	0		0
Fair value of real estate securities	320,865		342,171
GNMA interest-only
Schedule of Available-for-sale Securities [Line Items]
Within 1 year	172		0
1-5 years	14,691		15,914
5-10 years	713		724
After 10 years	49		183
Fair value of real estate securities	15,625		16,821
Agency securities
Schedule of Available-for-sale Securities [Line Items]
Within 1 year	0		0
1-5 years	771		780
5-10 years	0		0
After 10 years	0		0
Fair value of real estate securities	771		780
GNMA permanent securities
Schedule of Available-for-sale Securities [Line Items]
Within 1 year	1,593		0
1-5 years	2,086		4,488
5-10 years	35,790		27,675
After 10 years	0		7,617
Fair value of real estate securities	$ 39,469		$ 39,780

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=65884222&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=73527792&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=66010992&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=73527792&loc=d3e27161-111563

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