Fair Value of Financial Instruments - Valuation Methodologies Used for Instruments Measured at Fair Value on Non-Recurring Basis (Detail) (Fair Value, Measurements, Nonrecurring, USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Fair Value | Impaired Loans (collateral dependent)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset fair value	$ 17,703	$ 22,885
Fair Value | Other real estate owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset fair value	7,684	7,882
Significant Unobservable Inputs (Level 3) | Impaired Loans (collateral dependent)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset fair value	17,703	22,885
Significant Unobservable Inputs (Level 3) | Other real estate owned
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Asset fair value	$ 7,684	$ 7,882