Fair Values of Assets and Liabilities - Valuation Assumption Ranges for Derivative Commitments (Detail) - Derivative Mortgage Loans Commitments [Member]	Sep. 30, 2015
Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected loan close rate	25.00%
Inherent MSR value (basis points per loan)	47.00%
Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected loan close rate	100.00%
Inherent MSR value (basis points per loan)	193.00%
Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected loan close rate	75.00%
Inherent MSR value (basis points per loan)	116.00%