Fair Value - Significant Unobservable Inputs Used for Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail)	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Jun. 30, 2015	Dec. 31, 2014
Weighted Average [Member] | Excess Servicing Spread [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Weighted-average remaining life in years		6 years 10 months 7 days	7 years 3 months 18 days
Fair Value Inputs, Discount Rate		13.85%	13.60%
Conditional prepayment rate		9.53%	7.79%
Conditional default rate		0.39%	1.51%
Weighted Average [Member] | Mortgage-Backed Debt Related to Non-Residual Trusts [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate		6.00%	6.00%
Conditional prepayment rate		2.54%	2.72%
Conditional default rate		2.43%	2.55%
Loss severity		84.25%	82.87%
Weighted Average [Member] | HMBS Related Obligations [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Weighted-average remaining life in years		3 years 8 months	3 years 11 months
Conditional repayment rate		22.95%	21.21%
Fair Value Inputs, Discount Rate		2.07%	2.36%
Weighted Average [Member] | Interest Rate Lock Commitments [Member] | Derivative Financial Instruments, Liabilities [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Loan funding probability		81.58%	80.90%
Fair Value Of Servicing Rights Liabilities Embedded In Interest Rate Lock Commitments		4.27	4.06
Weighted Average [Member] | Loans Receivable [Member] | Reverse Loans [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Weighted-average remaining life in years		4 years 5 months 1 day	4 years 8 months
Conditional repayment rate		23.86%	21.68%
Fair Value Inputs, Discount Rate		2.61%	2.76%
Weighted Average [Member] | Loans Receivable [Member] | Forward Loans in Non-Residual Trusts [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate		8.00%	8.00%
Conditional prepayment rate		3.07%	3.17%
Conditional default rate		2.24%	2.34%
Loss severity		87.54%	85.88%
Weighted Average [Member] | Loans Receivable [Member] | Charged Off Loans [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate		30.18%	30.19%
Fair Value Inputs, Collection Rate		2.37%	2.46%
Weighted Average [Member] | Receivables Related to Non-Residual Trusts [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate		0.50%	0.50%
Conditional prepayment rate		2.54%	2.72%
Conditional default rate		2.43%	2.55%
Loss severity		84.25%	82.87%
Weighted Average [Member] | Servicing Rights Carried at Fair Value [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Weighted-average remaining life in years		6 years 3 months	6 years 7 months
Fair Value Inputs, Discount Rate		10.60%	9.55%
Conditional prepayment rate		9.73%	7.87%
Conditional default rate	1.05%	1.05%	2.36%
Weighted Average [Member] | Derivative Financial Instruments, Assets [Member] | Interest Rate Lock Commitments [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Loan funding probability		75.07%	77.45%
Fair value of servicing rights		3.78	3.83
Minimum [Member] | Excess Servicing Spread [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Weighted-average remaining life in years		6 years 8 months	7 years 2 months 12 days
Fair Value Inputs, Discount Rate		13.85%	13.60%
Conditional prepayment rate		8.61%	7.71%
Conditional default rate		0.22%	0.86%
Minimum [Member] | Mortgage-Backed Debt Related to Non-Residual Trusts [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate		6.00%	6.00%
Conditional prepayment rate		1.93%	1.89%
Conditional default rate		1.37%	1.92%
Loss severity		65.66%	73.26%
Minimum [Member] | HMBS Related Obligations [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Weighted-average remaining life in years		6 months	1 year 3 months 18 days
Conditional repayment rate		12.29%	11.30%
Fair Value Inputs, Discount Rate		1.26%	1.44%
Minimum [Member] | Interest Rate Lock Commitments [Member] | Derivative Financial Instruments, Liabilities [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Loan funding probability		2.34%	28.00%
Fair Value Of Servicing Rights Liabilities Embedded In Interest Rate Lock Commitments		0.01	0.67
Minimum [Member] | Loans Receivable [Member] | Reverse Loans [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Weighted-average remaining life in years		1 year 6 months	1 year 9 months 18 days
Conditional repayment rate		14.09%	13.40%
Fair Value Inputs, Discount Rate		1.86%	2.00%
Minimum [Member] | Loans Receivable [Member] | Forward Loans in Non-Residual Trusts [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate		8.00%	8.00%
Conditional prepayment rate		2.36%	2.24%
Conditional default rate		1.31%	1.68%
Loss severity		68.43%	76.12%
Minimum [Member] | Loans Receivable [Member] | Charged Off Loans [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate		30.00%	30.00%
Fair Value Inputs, Collection Rate		2.30%	2.34%
Minimum [Member] | Receivables Related to Non-Residual Trusts [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate		0.50%	0.50%
Conditional prepayment rate		1.93%	1.89%
Conditional default rate		1.37%	1.92%
Loss severity		65.66%	73.26%
Minimum [Member] | Servicing Rights Carried at Fair Value [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Weighted-average remaining life in years		5 years 6 months	5 years 7 months 6 days
Fair Value Inputs, Discount Rate		9.32%	8.24%
Conditional prepayment rate		5.66%	5.04%
Conditional default rate		0.05%	0.28%
Minimum [Member] | Derivative Financial Instruments, Assets [Member] | Interest Rate Lock Commitments [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Loan funding probability		2.34%	3.44%
Fair value of servicing rights		0.01	0.20
Maximum [Member] | Excess Servicing Spread [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Weighted-average remaining life in years		7 years 1 month	7 years 4 months 24 days
Fair Value Inputs, Discount Rate		13.85%	13.60%
Conditional prepayment rate		10.73%	7.89%
Conditional default rate		0.65%	2.31%
Maximum [Member] | Mortgage-Backed Debt Related to Non-Residual Trusts [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate		6.00%	6.00%
Conditional prepayment rate		3.44%	3.33%
Conditional default rate		3.46%	3.81%
Loss severity		90.85%	89.78%
Maximum [Member] | HMBS Related Obligations [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Weighted-average remaining life in years		6 years 8 months	7 years 8 months 12 days
Conditional repayment rate		51.65%	48.65%
Fair Value Inputs, Discount Rate		2.91%	3.06%
Maximum [Member] | Interest Rate Lock Commitments [Member] | Derivative Financial Instruments, Liabilities [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Loan funding probability		100.00%	100.00%
Fair Value Of Servicing Rights Liabilities Embedded In Interest Rate Lock Commitments		8.04	5.47
Maximum [Member] | Loans Receivable [Member] | Reverse Loans [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Weighted-average remaining life in years		10 years	12 years 3 months 18 days
Conditional repayment rate		45.38%	42.20%
Fair Value Inputs, Discount Rate		4.93%	3.65%
Maximum [Member] | Loans Receivable [Member] | Forward Loans in Non-Residual Trusts [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate		8.00%	8.00%
Conditional prepayment rate		3.98%	3.76%
Conditional default rate		3.20%	3.51%
Loss severity		94.22%	92.53%
Maximum [Member] | Loans Receivable [Member] | Charged Off Loans [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate		32.25%	32.25%
Fair Value Inputs, Collection Rate		3.47%	4.53%
Maximum [Member] | Receivables Related to Non-Residual Trusts [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Fair Value Inputs, Discount Rate		0.50%	0.50%
Conditional prepayment rate		3.44%	3.33%
Conditional default rate		3.46%	3.81%
Loss severity		90.85%	89.78%
Maximum [Member] | Servicing Rights Carried at Fair Value [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Weighted-average remaining life in years		9 years 6 months	9 years 3 months 18 days
Fair Value Inputs, Discount Rate		14.33%	29.16%
Conditional prepayment rate		12.02%	11.15%
Conditional default rate		2.16%	3.53%
Maximum [Member] | Derivative Financial Instruments, Assets [Member] | Interest Rate Lock Commitments [Member]
Fair Value Inputs Assets Liabilities Quantitative Information [Line Items]
Loan funding probability		100.00%	100.00%
Fair value of servicing rights		7.64	5.47