Variable Interest Entities - Additional Information (Detail) (USD $)	6 Months Ended
	Jun. 30, 2013 Trust	Dec. 31, 2012
Variable Interest Entity [Line Items]
Outstanding balance of collateral for mandatory clean-up call obligation	$ 418,300,000
VIE Primary Beneficiary [Member] | Residual Trusts [Member]
Variable Interest Entity [Line Items]
Number of securitization trusts related to Residual Trusts	12
VIE Primary Beneficiary [Member] | Non-Residual Trusts [Member]
Variable Interest Entity [Line Items]
Number of securitization trusts related to Non-Residual Trusts	10
Mandatory clean-up calls must be performed on the Non-Residual trusts when each loan pool falls to this percent of the original principal balance	10.00%
Expected period to exercise mandatory clean-up call obligation	2017 and continuing through 2019
Outstanding balance of collateral for mandatory clean-up call obligation	418,300,000
Number of securitization trusts consolidated and not consolidated with reimbursement obligations	7
VIE [Member]
Variable Interest Entity [Line Items]
Aggregate number of securitization trusts consolidated and not consolidated with reimbursement obligations	11
Reimbursement obligation of LOC, if drawn	165,000,000
Amount of LOCs available for eleven securitization trusts	280,800,000	285,400,000
VIE Not Primary Beneficiary [Member] | Servicing Arrangements with Loc Reimbursement Obligation [Member]
Variable Interest Entity [Line Items]
Number of securitization trusts consolidated and not consolidated with reimbursement obligations	4
Unpaid Principal Balance of Total Assets of Unconsolidated VIEs	$ 210,362,000	$ 223,251,000