Securities Available-for-Sale - Estimated Maturity Distribution of Securities Available-for-Sale (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Within one year, Amortized Cost	$ 39,726
After one but within five years, Amortized Cost	123,800
After five but within ten years, Amortized Cost	90,050
More than ten years, Amortized Cost	38,123
Amortized Cost	291,699	$ 336,751
Within one year, Fair Value	39,725
After one but within five years, Fair Value	123,830
After five but within ten years, Fair Value	89,822
More than ten years, Fair Value	38,025
Total, Fair Value	$ 291,402	$ 336,759