Fair Values of Assets and Liabilities - Valuation Assumption Ranges for Derivative Commitments (Detail)	Mar. 31, 2013 BasisPoint
Minimum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected loan close rate	28.00%
Inherent MSR value (basis points per loan)	52
Maximum [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected loan close rate	100.00%
Inherent MSR value (basis points per loan)	198
Average [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Expected loan close rate	78.00%
Inherent MSR value (basis points per loan)	111