Variable Interest Entities - Effect on Consolidated Cash Flow (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Amortization of deferred financing costs			$ 6,480	$ 1,294
Accretion (amortization) of securitized debt discounts/premiums, net			3,469	9,452
Payment of deferred financing costs			(8,073)
Proceeds from securitized debt borrowings, collateralized by loans held for investment			1,113,154
Payments on securitized debt borrowings, collateralized by loans held for investment			(292,568)	(61,054)
Proceeds from securitized debt borrowings, collateralized by Non-Agency RMBS				311,012
Payments on securitized debt borrowings, collateralized by Non-Agency RMBS			(380,432)	(520,730)
Decrease (increase) in accrued interest receivable			5,459	(6,591)
Increase (decrease) in accrued interest payable			(513)	(103)
Residential Mortgage Backed Securities transferred to consolidated VIEs [Member]
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Principal payments			394,641	541,348
Securitized Loans [Member]
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Principal payments			297,923	65,347
Variable Interest Entity, Primary Beneficiary [Member]
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Amortization of deferred financing costs	1,215	386	6,480	1,294
Accretion (amortization) of securitized debt discounts/premiums, net	4,352	2,949	3,469	9,452
Payment of deferred financing costs			(8,073)
Proceeds from securitized debt borrowings, collateralized by loans held for investment	11,628		1,113,154
Payments on securitized debt borrowings, collateralized by loans held for investment	(182,073)	(15,895)	(292,568)	(61,054)
Proceeds from securitized debt borrowings, collateralized by Non-Agency RMBS				311,012
Payments on securitized debt borrowings, collateralized by Non-Agency RMBS	(122,494)	(153,979)	(380,432)	(520,730)
Decrease (increase) in accrued interest receivable	927	(1,689)	1,401	(3,592)
Increase (decrease) in accrued interest payable	(1,080)	(861)	347	(1,241)
Net cash provided by/(used in) consolidated VIEs	27,119	4,036	1,136,342	341,836
Variable Interest Entity, Primary Beneficiary [Member] | Residential Mortgage Backed Securities transferred to consolidated VIEs [Member]
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Principal payments	130,869	156,180	394,641	541,348
Variable Interest Entity, Primary Beneficiary [Member] | Securitized Loans [Member]
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Principal payments	$ 183,775	$ 16,945	$ 297,923	$ 65,347