Annual report pursuant to Section 13 and 15(d)

Investment Securities - Realized Gains and Losses on Sales of Investment Securities (Detail)

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Investment Securities - Realized Gains and Losses on Sales of Investment Securities (Detail) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Amortized Cost and Fair Value Debt Securities [Abstract]      
Gross realized gains on sales of investment securities $ 2,012us-gaap_AvailableForSaleSecuritiesGrossRealizedGains $ 1,602us-gaap_AvailableForSaleSecuritiesGrossRealizedGains $ 1,447us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
Gross realized losses on sales of investment securities (1)us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses (563)us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses (51)us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses
Net realized gains on sales of investment securities 2,011us-gaap_AvailableForSaleSecuritiesGrossRealizedGainLossNet 1,039us-gaap_AvailableForSaleSecuritiesGrossRealizedGainLossNet 1,396us-gaap_AvailableForSaleSecuritiesGrossRealizedGainLossNet
Proceeds from sales of investment securities $ 169,533us-gaap_ProceedsFromSaleAndMaturityOfAvailableForSaleSecurities $ 78,473us-gaap_ProceedsFromSaleAndMaturityOfAvailableForSaleSecurities $ 102,538us-gaap_ProceedsFromSaleAndMaturityOfAvailableForSaleSecurities