Variable Interest Entities - Effect on Consolidated Financial Condition (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Assets
Accrued interest receivable	$ 17,767	$ 22,709	[1]
Liabilities
Accrued interest payable	2,434	3,294	[1]
Variable Interest Entity, Primary Beneficiary [Member]
Assets
Non-Agency RMBS transferred to consolidated VIEs	3,235,572	3,270,332
Securitized loans held for investment	1,136,923	256,632
Accrued interest receivable	25,215	26,616
Liabilities
Securitized debt, collateralized by Non-Agency RMBS	1,252,752	1,630,276
Securitized debt, collateralized by loans held for investment	1,033,925	212,778
Accrued interest payable	$ 8,477	$ 8,130

[1] Derived from the audited consolidated financial statements.