Quarterly report pursuant to Section 13 or 15(d)

Investment Securities - Additional Information (Detail)

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Investment Securities - Additional Information (Detail) (USD $)
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2014
Jun. 30, 2013
Jun. 30, 2014
Jun. 30, 2013
Dec. 31, 2013
Investment Securities [Line Items]          
Other-than-temporary impairment charge     $ 0   $ 0
Impairment charges on securities in continuous unrealized loss position for 12 months or longer 0   0   0
Net realized gain (loss) on redemption or sale of investment securities 364,000 303,000 1,785,000 312,000  
Recognized in earnings resulting from the redemption of investment securities 100,000 812,000 177,000 856,000  
Investment securities available-for-sale, carrying values 505,977,000   505,977,000   530,926,000
Collateralized mortgage obligations [Member]
         
Investment Securities [Line Items]          
Investment securities available-for-sale, carrying values 159,625,000   159,625,000   127,693,000
Mortgage-backed securities [Member]
         
Investment Securities [Line Items]          
Investment securities available-for-sale, carrying values 214,635,000   214,635,000   217,059,000
Mortgage-backed securities [Member] | Collateralized mortgage obligations [Member]
         
Investment Securities [Line Items]          
contractual maturities     2063    
Securities Pledged as Collateral [Member]
         
Investment Securities [Line Items]          
Investment securities available-for-sale, carrying values $ 69,700,000   $ 69,700,000   $ 47,600,000