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Securities - Amortized Cost and Fair Value of Debt Securities, by Contractual Maturity (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Available For Sale Securities Debt Maturities [Abstract]
Amortized Cost, One year or less	$ 22,734
Amortized Cost, After one year through five years	79,589
Amortized Cost, After five years through ten years	50,835
Amortized Cost, After ten years	3,044
Amortized Cost, Total	156,202
Amortized Cost, Mortgage-backed securities	36,416
Amortized Cost	192,618	$ 199,165
Fair Value, One year or less	22,674
Fair Value, After one year through five years	78,096
Fair Value, After five years through ten years	48,566
Fair Value, After ten years	2,864
Fair Value, Total	152,200
Fair Value, Mortgage-backed securities	34,836
Total, Fair Value	$ 187,036	$ 196,398

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