Investment Securities - Summary of Contractual Maturities of Investment Securities Classified as Available for Sale and Held to Maturity (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Available for Sale, Amortized Cost
Due in one year or less	$ 31,780
Due after one year through five years	109,529
Due after five years through ten years	31,360
Due after ten years	16,958
Total	189,627
Total securities	661,284	$ 649,741
Available for Sale, Fair Value
Due in one year or less	31,718
Due after one year through five years	110,039
Due after five years through ten years	31,890
Due after ten years	16,689
Total	190,336
Total securities	664,122	638,618
Held to Maturity, Amortized Cost
Due in one year or less	3,806
Due after one year through five years	41,579
Due after five years through ten years	25,483
Due after ten years	1,268
Total	72,136
Total securities	160,328	153,646
Held to Maturity, Fair Value
Due in one year or less	3,812
Due after one year through five years	41,893
Due after five years through ten years	25,646
Due after ten years	1,272
Total	72,623
Total securities	161,028	$ 150,932
Mortgage-backed securities
Available for Sale, Amortized Cost
Mortgage-backed securities	471,657
Available for Sale, Fair Value
Mortgage-backed securities	473,786
Held to Maturity, Amortized Cost
Mortgage-backed securities	88,192
Held to Maturity, Fair Value
Mortgage-backed securities	$ 88,405