v2.4.0.6
Securities - Additional Information (Detail) (USD $)
9 Months Ended
Sep. 30, 2012
Sep. 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 securities 203,000 231,000  
Number of securities in portfolio 227    
Number of securities in unrealized loss position 11    
Securities in unrealized loss position 131,000   101,000
Mortgage-backed securities issued by U.S. government sponsored entities 100.00%    
Carrying value of securities pledged to secure public deposits and repurchase agreements $ 327,242,000   $ 342,288,000