Geographic Concentrations of Credit Risk Exceeding 5% of Total Loan Balances (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2016 USD ($)
Concentration Risk [Line Items]
Principal Balance	$ 3,995,065
Securitized Loans [Member] | Credit Concentration Risk [Member]
Concentration Risk [Line Items]
Percentage Balance	100.00%
TEXAS
Concentration Risk [Line Items]
Principal Balance	$ 749,569
TEXAS | Securitized Loans [Member] | Credit Concentration Risk [Member]
Concentration Risk [Line Items]
Percentage Balance	18.80%
NORTH CAROLINA
Concentration Risk [Line Items]
Principal Balance	$ 537,375
NORTH CAROLINA | Securitized Loans [Member] | Credit Concentration Risk [Member]
Concentration Risk [Line Items]
Percentage Balance	13.50%
MARYLAND
Concentration Risk [Line Items]
Principal Balance	$ 499,495
MARYLAND | Securitized Loans [Member] | Credit Concentration Risk [Member]
Concentration Risk [Line Items]
Percentage Balance	12.50%
FLORIDA
Concentration Risk [Line Items]
Principal Balance	$ 456,663
FLORIDA | Securitized Loans [Member] | Credit Concentration Risk [Member]
Concentration Risk [Line Items]
Percentage Balance	11.40%
Other
Concentration Risk [Line Items]
Principal Balance	$ 1,751,963
Other | Securitized Loans [Member] | Credit Concentration Risk [Member]
Concentration Risk [Line Items]
Percentage Balance	43.80%