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Investment Securities - Additional Information (Detail) - USD ($)
$ in Thousands
6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]      
Held-to-maturity Securities Pledged as Collateral $ 296,300   $ 119,200
Proceeds from Sale of Available-for-sale Securities 103,618 $ 55,744  
Available-for-sale securities pledged as collateral $ 517,200   $ 445,800