Schedule of Quantitative Information about Level 3 Inputs Used to Measure Fair Value of Available for Sale Securities (Detail)	9 Months Ended
	Sep. 30, 2012
Residential mortgage-backed securities
Fair Value Assets Measured On Recurring Basis [Line Items]
Prepayment rate, Weighted Average of unobservable inputs	15.90%
Default rate, Weighted Average of unobservable inputs	9.10%
Loss severity, Weighted Average of unobservable inputs	51.20%
Trust preferred securities
Fair Value Assets Measured On Recurring Basis [Line Items]
Loss severity, Weighted Average of unobservable inputs	28.40%
Market credit spreads, Weighted Average of unobservable inputs	6.40%
Discount rate, Weighted Average of unobservable inputs	7.50%
Minimum | Residential mortgage-backed securities
Fair Value Assets Measured On Recurring Basis [Line Items]
Prepayment rate, Range of unobservable inputs	8.90%
Default rate, Range of unobservable inputs	4.00%
Loss severity, Range of unobservable inputs	40.00%
Minimum | Trust preferred securities
Fair Value Assets Measured On Recurring Basis [Line Items]
Loss severity, Range of unobservable inputs	0.00%
Market credit spreads, Range of unobservable inputs	6.00%
Discount rate, Range of unobservable inputs	6.40%
Maximum | Residential mortgage-backed securities
Fair Value Assets Measured On Recurring Basis [Line Items]
Prepayment rate, Range of unobservable inputs	29.20%
Default rate, Range of unobservable inputs	24.90%
Loss severity, Range of unobservable inputs	59.40%
Maximum | Trust preferred securities
Fair Value Assets Measured On Recurring Basis [Line Items]
Loss severity, Range of unobservable inputs	100.00%
Market credit spreads, Range of unobservable inputs	6.60%
Discount rate, Range of unobservable inputs	8.30%