Securities - Amortized Cost and Fair Value of Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Amortized Cost, Due in one year or less	$ 4,800
Amortized Cost, Due after one year through five years	33,657
Amortized Cost, Due after five years through ten years	31,566
Amortized Cost, Due after ten years	70,478
Amortized Cost, Mortgage-backed securities	84,266
Amortized Cost, Equity securities	481
Amortized Cost	225,248	$ 192,820
Fair value, Due in one year or less	4,801
Fair value, Due after one year through five years	33,779
Fair value, Due after five years through ten years	33,177
Fair value, Due after ten years	72,948
Fair value, Mortgage-backed securities	84,735
Fair value, Equity securities	757
Fair value, Total securities available for sale	$ 230,197	$ 195,864