Securities - Summary of Amortized Cost and Fair Value of Debt Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Available-for-sale
Due in one year or less, Amortized Cost	$ 5,067
Due after one through five years, Amortized Cost	17,212
Due after five through ten years, Amortized Cost	29,162
Due after ten years, Amortized Cost	44,611
Total debt securities available-for-sale, Amortized Cost	96,052
Due in one year or less, Fair Value	5,060
Due after one through five years, Fair Value	17,040
Due after five through ten years, Fair Value	28,586
Due after ten years, Fair Value	43,512
Total debt securities available-for-sale, Fair Value	94,198
Held-to-maturity
Due in one year or less, Amortized Cost	0
Due after one through five years, Amortized Cost	480
Due after five through ten years, Amortized Cost	3,000
Due after ten years, Amortized Cost	19,008
Amortized Cost, Held to maturity	22,488	$ 25,758
Due in one year or less, Fair Value	0
Due after one through five years, Fair Value	488
Due after five through ten years, Fair Value	2,831
Due after ten years, Fair Value	18,552
Total debt securities held-to-maturity, Fair Value	$ 21,871	$ 25,491