Fair Value of Assets and Liabilities - Quantitative Information about Significant Unobservable Inputs Used for Fair Value Measurements (Detail)	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Fair Value Inputs [Abstract]
Base market servicing rates (% per annum on unpaid principal balance)		0.50%
Total market servicing rate	0.57%
Level 3 Inputs | Minimum | Loans, notes and certificates
Fair Value Inputs [Abstract]
Discount rates	3.00%	2.90%
Net cumulative expected loss rates	0.30%	0.30%
Cumulative prepayment rates	8.00%	23.40%
Level 3 Inputs | Minimum | Servicing asset/liability
Fair Value Inputs [Abstract]
Discount rates	3.50%	3.50%
Net cumulative expected loss rates	0.30%	0.30%
Cumulative prepayment rates	8.00%	8.00%
Base market servicing rates (% per annum on unpaid principal balance)		0.50%
Total market servicing rate	0.57%
Level 3 Inputs | Maximum | Loans, notes and certificates
Fair Value Inputs [Abstract]
Discount rates	22.70%	17.50%
Net cumulative expected loss rates	27.50%	22.00%
Cumulative prepayment rates	44.30%	36.40%
Level 3 Inputs | Maximum | Servicing asset/liability
Fair Value Inputs [Abstract]
Discount rates	21.60%	16.30%
Net cumulative expected loss rates	27.50%	22.00%
Cumulative prepayment rates	44.30%	36.40%
Base market servicing rates (% per annum on unpaid principal balance)		0.75%
Total market servicing rate	0.90%
Level 3 Inputs | Weighted- Average | Loans, notes and certificates
Fair Value Inputs [Abstract]
Discount rates	8.10%	9.00%
Net cumulative expected loss rates	11.60%	9.90%
Cumulative prepayment rates	32.60%	30.80%
Level 3 Inputs | Weighted- Average | Servicing asset/liability
Fair Value Inputs [Abstract]
Discount rates	9.00%	9.40%
Net cumulative expected loss rates	9.70%	8.80%
Cumulative prepayment rates	36.60%	30.50%
Base market servicing rates (% per annum on unpaid principal balance)		0.50%
Total market servicing rate	0.57%	0.57%
Ancillary fee		0.07%