Summary of Accrued Interest Payable on Asset-Backed Securities Issued (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Accrued interest payable	$ 8,682	$ 4,592
Asset-backed Securities | Variable Interest Entity, Primary Beneficiary
Debt Instrument [Line Items]
Accrued interest payable	2,290	2,975
Asset-backed Securities | Variable Interest Entity, Primary Beneficiary | Sequoia
Debt Instrument [Line Items]
Accrued interest payable	1,509	2,103
Asset-backed Securities | Variable Interest Entity, Primary Beneficiary | Resecuritization
Debt Instrument [Line Items]
Accrued interest payable	33	40
Asset-backed Securities | Variable Interest Entity, Primary Beneficiary | Commercial Securitization
Debt Instrument [Line Items]
Accrued interest payable	$ 748	$ 832