Assets Measured at Fair Value on Non-Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fair Value Of Assets And Liabilities Measured At Non Recurring Basis [Line Items]
Impaired loans	$ 26,160	$ 26,309
Fair Value, Measurements, Non-Recurring [Member]
Fair Value Of Assets And Liabilities Measured At Non Recurring Basis [Line Items]
Impaired loans	11,374	5,178
Other real estate owned	123	924
Total	11,497	6,102
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value, Measurements, Non-Recurring [Member]
Fair Value Of Assets And Liabilities Measured At Non Recurring Basis [Line Items]
Impaired loans
Other real estate owned
Total
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Non-Recurring [Member]
Fair Value Of Assets And Liabilities Measured At Non Recurring Basis [Line Items]
Impaired loans
Other real estate owned
Total
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Non-Recurring [Member]
Fair Value Of Assets And Liabilities Measured At Non Recurring Basis [Line Items]
Impaired loans	11,374	5,178
Other real estate owned	123	924
Total	11,497	6,102
Total Gains (Losses) Recognized [Member] | Fair Value, Measurements, Non-Recurring [Member]
Fair Value Of Assets And Liabilities Measured At Non Recurring Basis [Line Items]
Impaired loans	(1,759)	1,756
Other real estate owned		(455)
Total	$ (1,759)	$ 1,301