REAL ESTATE SECURITIES - Securities by Remaining Maturity (Details) - USD ($)	3 Months Ended	6 Months Ended
Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Within 1 year	$ 612,682,000		$ 612,682,000		$ 612,752,000
1-5 years	1,620,503,000		1,620,503,000		1,260,381,000
5-10 years	459,348,000		459,348,000		533,604,000
After 10 years	7,677,000		7,677,000		480,000
Fair value of real estate securities	2,700,210,000		2,700,210,000		2,407,217,000
Other than temporary impairments included in consolidated statements of income	0	$ (900,000)	(600,000)	$ (1,400,000)
CMBS
Schedule of Available-for-sale Securities [Line Items]
Within 1 year	612,680,000		612,680,000		610,526,000
1-5 years	1,259,668,000		1,259,668,000		891,752,000
5-10 years	429,932,000		429,932,000		489,228,000
After 10 years	0		0		0
Fair value of real estate securities	2,302,280,000		2,302,280,000		1,991,506,000
CMBS interest-only
Schedule of Available-for-sale Securities [Line Items]
Within 1 year	0		0		0
1-5 years	334,613,000		334,613,000		344,423,000
5-10 years	0		0		0
After 10 years	0		0		0
Fair value of real estate securities	334,613,000		334,613,000		344,423,000
GNMA interest-only
Schedule of Available-for-sale Securities [Line Items]
Within 1 year	2,000		2,000		6,000
1-5 years	19,540,000		19,540,000		17,159,000
5-10 years	1,138,000		1,138,000		8,549,000
After 10 years	153,000		153,000		480,000
Fair value of real estate securities	20,833,000		20,833,000		26,194,000
GNMA construction securities
Schedule of Available-for-sale Securities [Line Items]
Within 1 year					0
1-5 years					386,000
5-10 years					28,253,000
After 10 years					0
Fair value of real estate securities					28,639,000
GNMA permanent securities
Schedule of Available-for-sale Securities [Line Items]
Within 1 year	0		0		2,220,000
1-5 years	6,682,000		6,682,000		6,661,000
5-10 years	28,278,000		28,278,000		7,574,000
After 10 years	7,524,000		7,524,000		0
Fair value of real estate securities	$ 42,484,000		$ 42,484,000		$ 16,455,000

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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