Fair Value - Schedule of Significant Unobservable Inputs Used in Fair Value Measurement of Assets and Liabilities on Recurring Basis (Detail) - Recurring Measurement Basis - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Freestanding Derivative Instruments | Interest Rate Lock Commitments | Minimum
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Loan funding probability	21.18%	34.40%
Fair value of initial servicing rights multiple	0.21	0.04
Freestanding Derivative Instruments | Interest Rate Lock Commitments | Maximum
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Loan funding probability	100.00%	100.00%
Fair value of initial servicing rights multiple	5.08	6.04
Freestanding Derivative Instruments | Interest Rate Lock Commitments | Weighted Average
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Loan funding probability	83.12%	83.36%
Fair value of initial servicing rights multiple	3.39	3.69
Mortgage-Backed Debt Related to Non-Residual Trusts | Minimum
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Discount rate	6.00%	6.00%
Conditional prepayment rate	2.37%	2.22%
Conditional default rate	2.60%	2.32%
Loss severity	86.18%	77.88%
Mortgage-Backed Debt Related to Non-Residual Trusts | Maximum
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Discount rate	6.00%	6.00%
Conditional prepayment rate	3.23%	3.17%
Conditional default rate	5.87%	4.66%
Loss severity	100.00%	100.00%
Mortgage-Backed Debt Related to Non-Residual Trusts | Weighted Average
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Discount rate	6.00%	6.00%
Conditional prepayment rate	2.83%	2.65%
Conditional default rate	3.78%	3.34%
Loss severity	97.41%	94.51%
HMBS Related Obligations | Minimum
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Weighted-average remaining life in years	2 months 12 days	4 months 24 days
Conditional repayment rate	11.10%	11.49%
Discount rate	1.47%	1.50%
HMBS Related Obligations | Maximum
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Weighted-average remaining life in years	7 years 7 months 6 days	7 years 2 months 12 days
Conditional repayment rate	76.13%	57.76%
Discount rate	3.12%	3.17%
HMBS Related Obligations | Weighted Average
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Weighted-average remaining life in years	3 years 2 months 12 days	3 years 2 months
Conditional repayment rate	30.09%	27.74%
Discount rate	2.70%	2.56%
Reverse Loans | Minimum
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Weighted-average remaining life in years	3 months 18 days	7 months 6 days
Conditional repayment rate	12.81%	13.23%
Discount rate	1.81%	1.93%
Reverse Loans | Maximum
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Weighted-average remaining life in years	10 years 2 months 12 days	10 years 2 months 12 days
Conditional repayment rate	70.80%	55.32%
Discount rate	3.65%	3.69%
Reverse Loans | Weighted Average
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Weighted-average remaining life in years	3 years 7 months 6 days	3 years 9 months 18 days
Conditional repayment rate	30.91%	28.48%
Discount rate	3.05%	2.93%
Mortgage Loans Related to Non-Residual Trusts | Minimum
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Discount rate	8.00%	8.00%
Conditional prepayment rate	1.97%	1.98%
Conditional default rate	1.06%	1.02%
Loss severity	87.95%	79.98%
Mortgage Loans Related to Non-Residual Trusts | Maximum
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Discount rate	8.00%	8.00%
Conditional prepayment rate	2.52%	2.67%
Conditional default rate	5.17%	4.25%
Loss severity	100.00%	100.00%
Mortgage Loans Related to Non-Residual Trusts | Weighted Average
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Discount rate	8.00%	8.00%
Conditional prepayment rate	2.28%	2.27%
Conditional default rate	2.87%	2.61%
Loss severity	99.04%	96.61%
Mortgage Loans Held For Sale | Minimum
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Discount rate	8.00%
Conditional prepayment rate	2.10%
Conditional default rate	1.49%
Loss severity	85.57%
Mortgage Loans Held For Sale | Maximum
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Discount rate	8.00%
Conditional prepayment rate	2.10%
Conditional default rate	1.49%
Loss severity	85.57%
Mortgage Loans Held For Sale | Weighted Average
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Discount rate	8.00%
Conditional prepayment rate	2.10%
Conditional default rate	1.49%
Loss severity	85.57%
Charged-Off Loans | Minimum
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Discount rate	28.00%	28.00%
Collection rate	3.04%	2.69%
Charged-Off Loans | Maximum
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Discount rate	28.00%	28.00%
Collection rate	5.15%	3.55%
Charged-Off Loans | Weighted Average
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Discount rate	28.00%	28.00%
Collection rate	3.15%	2.74%
Receivables Related to Non-Residual Trusts | Minimum
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Discount rate	0.50%	0.50%
Conditional prepayment rate	2.37%	2.22%
Conditional default rate	2.60%	2.32%
Loss severity	86.18%	77.88%
Receivables Related to Non-Residual Trusts | Maximum
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Discount rate	0.50%	0.50%
Conditional prepayment rate	3.23%	3.17%
Conditional default rate	5.87%	4.66%
Loss severity	100.00%	100.00%
Receivables Related to Non-Residual Trusts | Weighted Average
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Discount rate	0.50%	0.50%
Conditional prepayment rate	2.83%	2.65%
Conditional default rate	3.78%	3.34%
Loss severity	97.41%	94.51%
Servicing Rights Carried at Fair Value | Minimum
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Weighted-average remaining life in years	2 years 5 months 18 days	2 years 7 months 6 days
Discount rate	10.62%	10.68%
Conditional prepayment rate	6.08%	5.76%
Conditional default rate	0.02%	0.04%
Cost to service	$ 62	$ 62
Servicing Rights Carried at Fair Value | Maximum
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Weighted-average remaining life in years	7 years 1 month 21 days	7 years 4 months 24 days
Discount rate	15.22%	14.61%
Conditional prepayment rate	23.87%	21.67%
Conditional default rate	3.21%	2.97%
Cost to service	$ 1,260	$ 1,260
Servicing Rights Carried at Fair Value | Weighted Average
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Weighted-average remaining life in years	5 years 10 months 24 days	6 years
Discount rate	11.97%	11.56%
Conditional prepayment rate	9.82%	9.09%
Conditional default rate	0.85%	0.88%
Cost to service	$ 132	$ 128
Freestanding Derivative Instruments | Interest Rate Lock Commitments | Minimum
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Loan funding probability	1.00%	16.00%
Fair value of initial servicing rights multiple	0.01	0.01
Freestanding Derivative Instruments | Interest Rate Lock Commitments | Maximum
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Loan funding probability	100.00%	100.00%
Fair value of initial servicing rights multiple	5.16	5.98
Freestanding Derivative Instruments | Interest Rate Lock Commitments | Weighted Average
Significant Unobservable Inputs Used In Fair Value Measurement [Line Items]
Loan funding probability	64.94%	75.86%
Fair value of initial servicing rights multiple	2.67	3.06