Fair Value Measurements - Unobservable Inputs Assumptions - Securitized Loans Held for Investment (Detail) - Fair Value, Inputs, Level 3 [Member] - Securitized Loans Held for Investment at Fair Value [Member] - Point	Mar. 31, 2016	Dec. 31, 2015
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Owner Occupied	96.00%	96.00%
Investor	4.00%	4.00%
Secondary	0.00%	0.00%
Single family	77.00%	77.00%
Manufactured housing	11.00%	11.00%
Multi-family/mixed use/other	12.00%	12.00%
Weighted Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
FICO	624	625
Loan-to-value (LTV)	81.00%	81.00%
Weighted Average [Member] | Clean [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Coupon	6.90%	6.90%
Weighted Average [Member] | Reperforming [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Coupon	6.60%	6.70%
Base Rate [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
FICO	620	620
Loan-to-value (LTV)	90.00%	90.00%
Base Rate [Member] | Clean [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Coupon	4.40%	4.40%
Base Rate [Member] | Reperforming [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Coupon	5.30%	5.30%