Fair Value - Schedule of Significant Unobservable Inputs Used in Fair Value Measurement of Assets and Liabilities on Recurring Basis (Detail) - Recurring Measurement Basis [Member] - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Freestanding Derivative Instruments [Member] | Interest Rate Lock Commitments [Member] | Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Loan funding probability	34.40%	38.00%
Fair value of initial servicing rights multiple	0.04	0.11
Freestanding Derivative Instruments [Member] | Interest Rate Lock Commitments [Member] | Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Loan funding probability	100.00%	100.00%
Fair value of initial servicing rights multiple	6.04	5.88
Freestanding Derivative Instruments [Member] | Interest Rate Lock Commitments [Member] | Weighted Average [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Loan funding probability	83.36%	83.28%
Fair value of initial servicing rights multiple	3.69	4.00
Servicing Rights Related Liabilities [Member] | Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Weighted-average remaining life in years		6 years 3 months 12 days
Discount rate		11.67%
Conditional prepayment rate		8.32%
Conditional default rate		0.11%
Servicing Rights Related Liabilities [Member] | Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Weighted-average remaining life in years		7 years 4 months 24 days
Discount rate		13.85%
Conditional prepayment rate		11.28%
Conditional default rate		1.06%
Servicing Rights Related Liabilities [Member] | Weighted Average [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Weighted-average remaining life in years		6 years 6 months 29 days
Discount rate		13.24%
Conditional prepayment rate		9.98%
Conditional default rate		0.58%
Mortgage-Backed Debt Related to Non-Residual Trusts [Member] | Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	6.00%	6.00%
Conditional prepayment rate	2.22%	1.93%
Conditional default rate	2.32%	1.66%
Loss severity	77.88%	70.33%
Mortgage-Backed Debt Related to Non-Residual Trusts [Member] | Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	6.00%	6.00%
Conditional prepayment rate	3.17%	3.62%
Conditional default rate	4.66%	2.98%
Loss severity	100.00%	93.46%
Mortgage-Backed Debt Related to Non-Residual Trusts [Member] | Weighted Average [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	6.00%	6.00%
Conditional prepayment rate	2.65%	2.90%
Conditional default rate	3.34%	2.30%
Loss severity	94.51%	85.63%
HMBS Related Obligations [Member] | Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Weighted-average remaining life in years	5 months	10 months 18 days
Conditional repayment rate	11.49%	12.06%
Discount rate	1.50%	1.73%
HMBS Related Obligations [Member] | Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Weighted-average remaining life in years	7 years 2 months 11 days	6 years 7 months 12 days
Conditional repayment rate	57.76%	55.49%
Discount rate	3.17%	3.08%
HMBS Related Obligations [Member] | Weighted Average [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Weighted-average remaining life in years	3 years 2 months	3 years 6 months
Conditional repayment rate	27.74%	24.70%
Discount rate	2.56%	2.39%
Reverse Loans [Member] | Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Weighted-average remaining life in years	7 months 5 days	1 year 1 month 6 days
Conditional repayment rate	13.23%	13.53%
Discount rate	1.93%	2.08%
Reverse Loans [Member] | Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Weighted-average remaining life in years	10 years 2 months 12 days	10 years
Conditional repayment rate	55.32%	52.94%
Discount rate	3.69%	3.56%
Reverse Loans [Member] | Weighted Average [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Weighted-average remaining life in years	3 years 9 months 18 days	4 years 22 days
Conditional repayment rate	28.48%	25.59%
Discount rate	2.93%	2.84%
Mortgage Loans Related To Non Residual Trusts [Member] | Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	8.00%	8.00%
Conditional prepayment rate	1.98%	2.67%
Conditional default rate	1.02%	1.47%
Loss severity	79.98%	73.07%
Mortgage Loans Related To Non Residual Trusts [Member] | Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	8.00%	8.00%
Conditional prepayment rate	2.67%	4.66%
Conditional default rate	4.25%	2.74%
Loss severity	100.00%	95.88%
Mortgage Loans Related To Non Residual Trusts [Member] | Weighted Average [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	8.00%	8.00%
Conditional prepayment rate	2.27%	3.52%
Conditional default rate	2.61%	2.05%
Loss severity	96.61%	88.72%
Charged-off Loans [Member] | Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	28.00%	28.00%
Collection rate	2.69%	2.15%
Charged-off Loans [Member] | Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	28.00%	28.00%
Collection rate	3.55%	3.54%
Charged-off Loans [Member] | Weighted Average [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	28.00%	28.00%
Collection rate	2.74%	2.23%
Receivables Related to Non-Residual Trusts [Member] | Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	0.50%	0.50%
Conditional prepayment rate	2.22%	1.93%
Conditional default rate	2.32%	1.66%
Loss severity	77.88%	70.33%
Receivables Related to Non-Residual Trusts [Member] | Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	0.50%	0.50%
Conditional prepayment rate	3.17%	3.62%
Conditional default rate	4.66%	2.98%
Loss severity	100.00%	93.46%
Receivables Related to Non-Residual Trusts [Member] | Weighted Average [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Discount rate	0.50%	0.50%
Conditional prepayment rate	2.65%	2.90%
Conditional default rate	3.34%	2.30%
Loss severity	94.51%	85.63%
Servicing Rights Carried at Fair Value [Member] | Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Weighted-average remaining life in years	2 years 7 months	5 years 2 months
Discount rate	10.68%	10.00%
Conditional prepayment rate	5.76%	6.07%
Conditional default rate	0.04%	0.05%
Cost to service	$ 62	$ 70
Servicing Rights Carried at Fair Value [Member] | Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Weighted-average remaining life in years	7 years 5 months	9 years
Discount rate	14.61%	14.34%
Conditional prepayment rate	21.67%	13.15%
Conditional default rate	2.97%	2.49%
Cost to service	$ 1,260	$ 455
Servicing Rights Carried at Fair Value [Member] | Weighted Average [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Weighted-average remaining life in years	6 years	6 years 4 months
Discount rate	11.56%	10.88%
Conditional prepayment rate	9.09%	9.94%
Conditional default rate	0.88%	1.06%
Cost to service	$ 128	$ 97
Freestanding Derivative Instruments [Member] | Interest Rate Lock Commitments [Member] | Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Loan funding probability	16.00%	2.34%
Fair value of initial servicing rights multiple	0.01	0.05
Freestanding Derivative Instruments [Member] | Interest Rate Lock Commitments [Member] | Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Loan funding probability	100.00%	100.00%
Fair value of initial servicing rights multiple	5.98	7.06
Freestanding Derivative Instruments [Member] | Interest Rate Lock Commitments [Member] | Weighted Average [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Loan funding probability	75.86%	79.42%
Fair value of initial servicing rights multiple	3.06	3.71