Real Estate Securities - Components of Carrying Value (Which Equals Fair Value) of Residential Available for Sale Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Carrying Value	$ 1,041,458	$ 1,267,624
Senior Securities
Schedule of Available-for-sale Securities [Line Items]
Carrying Value	445,336	487,557
Senior Securities | Prime
Schedule of Available-for-sale Securities [Line Items]
Carrying Value	278,960	307,813
Senior Securities | Non-prime
Schedule of Available-for-sale Securities [Line Items]
Carrying Value	166,376	179,744
Re-REMIC
Schedule of Available-for-sale Securities [Line Items]
Carrying Value	169,084	168,347
Subordinate Securities
Schedule of Available-for-sale Securities [Line Items]
Carrying Value	427,038	611,720
Subordinate Securities | Prime
Schedule of Available-for-sale Securities [Line Items]
Carrying Value	257,263	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	1,194,372	1,445,079
Credit reserve	(61,700)	(70,067)
Unamortized discount, net	(273,119)	(296,342)
Amortized cost	859,553	1,078,670
Gross unrealized gains	184,857	191,750
Gross unrealized losses	(2,952)	(2,796)
Carrying Value	1,041,458	1,267,624
Residential | Senior Securities | Prime
Schedule of Available-for-sale Securities [Line Items]
Principal balance	282,921	311,573
Credit reserve	(2,650)	(3,660)
Unamortized discount, net	(30,401)	(34,782)
Amortized cost	249,870	273,131
Gross unrealized gains	31,196	35,980
Gross unrealized losses	(2,106)	(1,298)
Carrying Value	278,960	307,813
Residential | Senior Securities | Non-prime
Schedule of Available-for-sale Securities [Line Items]
Principal balance	182,719	196,258
Credit reserve	(9,175)	(9,644)
Unamortized discount, net	(27,533)	(31,491)
Amortized cost	146,011	155,123
Gross unrealized gains	20,550	24,682
Gross unrealized losses	(185)	(61)
Carrying Value	166,376	179,744
Residential | Re-REMIC
Schedule of Available-for-sale Securities [Line Items]
Principal balance	193,221	195,098
Credit reserve	(13,071)	(15,202)
Unamortized discount, net	(75,658)	(79,611)
Amortized cost	104,492	100,285
Gross unrealized gains	64,592	68,062
Gross unrealized losses	0	0
Carrying Value	169,084	168,347
Residential | Subordinate Securities
Schedule of Available-for-sale Securities [Line Items]
Principal balance	535,511	742,150
Credit reserve	(36,804)	(41,561)
Unamortized discount, net	(139,527)	(150,458)
Amortized cost	359,180	550,131
Gross unrealized gains	68,519	63,026
Gross unrealized losses	(661)	(1,437)
Carrying Value	$ 427,038	$ 611,720