Securities - Summary of Amortized Cost and Fair Value of Debt Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Available-for-sale
Due in one year or less, Amortized Cost	$ 3,190
Due after one through five years, Amortized Cost	18,798
Due after five through ten years, Amortized Cost	26,083
Due after ten years, Amortized Cost	49,674
Total debt securities available-for-sale, Amortized Cost	97,745
Due in one year or less, Fair Value	3,208
Due after one through five years, Fair Value	18,917
Due after five through ten years, Fair Value	26,271
Due after ten years, Fair Value	49,562
Total debt securities available-for-sale, Fair Value	97,958
Held-to-maturity
Due in one year or less, Amortized Cost	4,700
Due after one through five years, Amortized Cost	477
Due after five through ten years, Amortized Cost	3,000
Due after ten years, Amortized cost	18,298
Amortized Cost, Held to maturity	26,475	$ 23,883
Due in one year or less, Fair Value	4,714
Due after one through five years, Fair Value	498
Due after five through ten years, Fair Value	2,914
Due after ten years, Fair Value	18,305
Total debt securities held-to-maturity, Fair Value	$ 26,431	$ 23,444