Fair Values of Assets and Liabilities - Valuation Assumption Ranges for Derivative Commitments (Detail) - Derivative Mortgage Loans Commitments [Member]	Sep. 30, 2016
Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected loan close rate	17.00%
Inherent MSR value (basis points per loan)	46.00%
Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected loan close rate	99.00%
Inherent MSR value (basis points per loan)	192.00%
Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected loan close rate	77.00%
Inherent MSR value (basis points per loan)	112.00%