Real Estate Securities - Components of Carrying Value (Which Equals Fair Value) of Residential Available for Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Carrying Value	$ 1,178,406us-gaap_AvailableForSaleSecurities	$ 1,267,624us-gaap_AvailableForSaleSecurities
Senior Securities
Schedule of Available-for-sale Securities [Line Items]
Carrying Value	472,746	487,557
Senior Securities \| Prime
Schedule of Available-for-sale Securities [Line Items]
Carrying Value	297,872	307,813
Senior Securities \| Non-prime
Schedule of Available-for-sale Securities [Line Items]
Carrying Value	174,874	179,744
Re-REMIC
Schedule of Available-for-sale Securities [Line Items]
Carrying Value	169,239	168,347
Subordinate Securities
Schedule of Available-for-sale Securities [Line Items]
Carrying Value	536,421	611,720
Subordinate Securities \| Prime
Schedule of Available-for-sale Securities [Line Items]
Carrying Value	370,391	448,838
Subordinate Securities \| Non-prime
Schedule of Available-for-sale Securities [Line Items]
Carrying Value	1,000	1,000
Residential
Schedule of Available-for-sale Securities [Line Items]
Principal balance	1,335,622	1,445,079
Credit reserve	(63,584)	(70,067)
Unamortized discount, net	(286,382)	(296,342)
Amortized cost	985,656	1,078,670
Gross unrealized gains	195,636	191,750
Gross unrealized losses	(2,886)	(2,796)
Carrying Value	1,178,406	1,267,624
Residential \| Senior Securities \| Prime
Schedule of Available-for-sale Securities [Line Items]
Principal balance	302,046	311,573
Credit reserve	(2,830)	(3,660)
Unamortized discount, net	(32,645)	(34,782)
Amortized cost	266,571	273,131
Gross unrealized gains	33,313	35,980
Gross unrealized losses	(2,012)	(1,298)
Carrying Value	297,872	307,813
Residential \| Senior Securities \| Non-prime
Schedule of Available-for-sale Securities [Line Items]
Principal balance	190,790	196,258
Credit reserve	(9,027)	(9,644)
Unamortized discount, net	(29,791)	(31,491)
Amortized cost	151,972	155,123
Gross unrealized gains	22,984	24,682
Gross unrealized losses	(82)	(61)
Carrying Value	174,874	179,744
Residential \| Re-REMIC
Schedule of Available-for-sale Securities [Line Items]
Principal balance	194,296	195,098
Credit reserve	(12,667)	(15,202)
Unamortized discount, net	(79,401)	(79,611)
Amortized cost	102,228	100,285
Gross unrealized gains	67,011	68,062
Gross unrealized losses	0	0
Carrying Value	169,239	168,347
Residential \| Subordinate Securities
Schedule of Available-for-sale Securities [Line Items]
Principal balance	648,490	742,150
Credit reserve	(39,060)	(41,561)
Unamortized discount, net	(144,545)	(150,458)
Amortized cost	464,885	550,131
Gross unrealized gains	72,328	63,026
Gross unrealized losses	(792)	(1,437)
Carrying Value	$ 536,421	$ 611,720

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

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- Definition

Available For Sale Securities Principal Balance

+ References

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- Definition

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

+ References

No definition available.

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- Definition

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

+ 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 (b)

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- Definition

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

+ References

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-Publisher FASB

-Name Accounting Standards Codification

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

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-Section 25

-Paragraph 1

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This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

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-Section S99

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