Securities - Additional Information (Detail) (USD $)
6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Dec. 31, 2011
Investment [Line Items]   
Proceeds from sale of available-for-sale securities$ 6,944,000$ 13,367,000 
Gains from sale of available-for-sale securities203,000231,000 
Gain on sale of securities, negative adjustment recorded as of settlement date4,000  
Number of securities in portfolio226  
Number of securities in unrealized loss position17  
Securities in unrealized loss position184,000 101,000
Mortgage-backed securities issued by U.S. government sponsored entities100.00%  
Carrying value of securities pledged to secure public deposits and repurchase agreements$ 340,071 $ 342,288