Securities - Summary of Amortized Cost and Fair Value of Debt Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Available-for-sale
Due in one year or less, Amortized Cost	$ 5,068
Due after one through five years, Amortized Cost	16,684
Due after five through ten years, Amortized Cost	28,245
Due after ten years, Amortized Cost	42,820
Total debt securities available-for-sale, Amortized Cost	92,817
Due in one year or less, Fair Value	5,060
Due after one through five years, Fair Value	16,467
Due after five through ten years, Fair Value	27,683
Due after ten years, Fair Value	41,598
Total debt securities available-for-sale, Fair Value	90,808
Held-to-maturity
Due in one year or less, Amortized Cost	0
Due after one through five years, Amortized Cost	481
Due after five through ten years, Amortized Cost	3,000
Due after ten years, Amortized Cost	18,401
Amortized Cost, Held to maturity	21,882	$ 25,758
Due in one year or less, Fair Value	0
Due after one through five years, Fair Value	485
Due after five through ten years, Fair Value	2,811
Due after ten years, Fair Value	17,877
Total debt securities held-to-maturity, Fair Value	$ 21,173	$ 25,491