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Investment Securities - Additional Information (Detail)
9 Months Ended
Sep. 30, 2015
USD ($)
security
Sep. 30, 2014
USD ($)
Dec. 31, 2014
USD ($)
Investments Debt And Equity Securities [Abstract]      
Number of debt securities continues loss position for more than twelve months | security 7    
Number of debt securities continues loss position for less than twelve months | security 77    
Investment securities available-for-sale carrying amount $ 52,100,000   $ 61,100,000
Gains realized on sales of securities available-for-sale 359,000 $ 103,000  
Losses on sales of securities $ 0 $ 0