Geographic Concentrations of Credit Risk Exceeding 5% of Total Loan Unpaid Principal Balances (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2016 USD ($)
Concentration Risk [Line Items]
Principal Balance	$ 3,994,946
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	$ 456,589
FLORIDA | Securitized Loans [Member] | Credit Concentration Risk [Member]
Concentration Risk [Line Items]
Percentage Balance	11.40%
Other
Concentration Risk [Line Items]
Principal Balance	$ 1,751,918
Other | Securitized Loans [Member] | Credit Concentration Risk [Member]
Concentration Risk [Line Items]
Percentage Balance	43.80%