Assets Measured at Fair Value on Non-Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Fair Value Of Assets And Liabilities Measured At Non Recurring Basis [Line Items]
Impaired loans	$ 27,330	$ 23,552
Fair Value, Measurements, Non-Recurring
Fair Value Of Assets And Liabilities Measured At Non Recurring Basis [Line Items]
Impaired loans	6,209	6,296
Other real estate owned	547	5,909
Total	6,756	12,505
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Non-Recurring
Fair Value Of Assets And Liabilities Measured At Non Recurring Basis [Line Items]
Impaired loans	6,209	6,296
Other real estate owned	547	5,909
Total	6,756	12,505
Total Gain(Losses) Recognized | Fair Value, Measurements, Non-Recurring
Fair Value Of Assets And Liabilities Measured At Non Recurring Basis [Line Items]
Impaired loans	1,272	(1,370)
Other real estate owned	(143)	(1,065)
Total	$ 1,129	$ (2,435)