Quarterly report pursuant to Section 13 or 15(d)

Securities - Schedule of Amortized Cost and Estimated Fair Value of Investment Securities by Contractual Maturity (Detail)

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Securities - Schedule of Amortized Cost and Estimated Fair Value of Investment Securities by Contractual Maturity (Detail) - USD ($)
$ in Thousands
Jun. 30, 2017
Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]    
Available-for-Sale Within one year, Amortized Cost $ 15,692  
Available-for-Sale Over one year through five years, Amortized Cost 59,465  
Available-for-Sale Over five years through ten years, Amortized Cost 249,990  
Available-for-Sale Over ten years, Amortized Cost 246,464  
Amortized Cost 571,611 $ 521,053
Available-for-Sale Within one year, Estimated Fair Value 15,648  
Available-for-Sale Over one year through five years, Estimated Fair Value 59,365  
Available-for-Sale Over five years through ten years, Estimated Fair Value 251,060  
Available-for-Sale Over ten years, Estimated Fair Value 245,773  
Securities available for sale $ 571,846 $ 516,964