Quantitative Information About Level 3 Fair Value Measurements for Financial Instruments Measured at Fair Value on Non-Recurring Basis (Detail) (Significant Unobservable Inputs (Level 3) [Member], Impaired Loans with Specific Allocations [Member], USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012
Commercial Real Estate [Member]
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Fair Value	$ 2,930
Valuation Technique(s)	Sales comparison approach Income approach Cost approach
Unobservable Input(s)	Adjustment for physical condition of comparable properties sold Adjustment for net operating income generated by the property Adjustment for investor rates of return
Commercial and Industrial [Member]
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Fair Value	$ 1,298
Valuation Technique(s)	Sales comparison approach.
Unobservable Input(s)	Adjustment for differences between the comparable sales
Minimum [Member] | Commercial Real Estate [Member]
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
(Weighted Average)	20.00%
Minimum [Member] | Commercial and Industrial [Member]
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
(Weighted Average)	4.00%
Maximum [Member] | Commercial Real Estate [Member]
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
(Weighted Average)	78.00%
Maximum [Member] | Commercial and Industrial [Member]
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
(Weighted Average)	58.00%
Weighted Average [Member] | Commercial Real Estate [Member]
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
(Weighted Average)	46.00%
Weighted Average [Member] | Commercial and Industrial [Member]
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
(Weighted Average)	8.00%