Real Estate Securities - Components of Carrying Value (Which Equals Fair Value) of Residential Available for Sale Securities (Details) - Residential - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Principal balance	$ 552,935	$ 608,145
Credit reserve	(40,616)	(46,549)
Unamortized discount, net	(178,302)	(183,753)
Amortized cost	334,017	377,843
Gross unrealized gains	117,593	131,190
Gross unrealized losses	(1,322)	(1,367)
Carrying Value	450,288	507,666
Senior IO Securities
Schedule of Available-for-sale Securities [Line Items]
Principal balance	172,026	189,125
Credit reserve	(8,206)	(8,756)
Unamortized discount, net	(39,174)	(44,041)
Amortized cost	124,646	136,328
Gross unrealized gains	41,919	44,771
Gross unrealized losses	(955)	(1,235)
Carrying Value	165,610	179,864
Mezzanine
Schedule of Available-for-sale Securities [Line Items]
Principal balance	67,995	91,471
Credit reserve	0	0
Unamortized discount, net	(6,959)	(9,407)
Amortized cost	61,036	82,064
Gross unrealized gains	6,255	9,938
Gross unrealized losses	0	0
Carrying Value	67,291	92,002
Subordinate Securities
Schedule of Available-for-sale Securities [Line Items]
Principal balance	312,914	327,549
Credit reserve	(32,410)	(37,793)
Unamortized discount, net	(132,169)	(130,305)
Amortized cost	148,335	159,451
Gross unrealized gains	69,419	76,481
Gross unrealized losses	(367)	(132)
Carrying Value	$ 217,387	$ 235,800

Balance of credit reserve on available-for-sale securities.

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Available For Sale Securities Principal Balance

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Balance of net unamortized discount on available-for-sale securities.

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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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
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Amount of debt securities categorized neither as held-to-maturity nor trading.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
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-URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558

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-Publisher FASB
-Name Accounting Standards Codification
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-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66010992&loc=d3e26610-111562

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-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 320
-Section 50
-Paragraph 2
-Subparagraph (b)-(g)
-URI http://asc.fasb.org/extlink&oid=6957658&loc=d3e62557-112803

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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