Investment Securities - Summary of Contractual Maturities of Investment Securities Classified as Available for Sale and Held to Maturity (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Available for Sale, Amortized Cost
Due in one year or less	$ 24,755
Due after one year through five years	116,056
Due after five years through ten years	32,550
Due after ten years	17,577
Total	190,938
Total securities	664,252
Available for Sale, Fair Value
Due in one year or less	24,636
Due after one year through five years	115,089
Due after five years through ten years	32,602
Due after ten years	17,275
Total	189,602
Total securities	659,238	$ 638,618
Held to Maturity, Amortized Cost
Due in one year or less	5,924
Due after one year through five years	42,423
Due after five years through ten years	24,379
Due after ten years	2,685
Total	75,411
Total securities	159,308	153,646
Held to Maturity, Fair Value
Due in one year or less	5,929
Due after one year through five years	42,361
Due after five years through ten years	24,144
Due after ten years	2,694
Total	75,128
Total securities	158,219	$ 150,932
Mortgage-backed securities
Available for Sale, Amortized Cost
Mortgage-backed securities	473,314
Available for Sale, Fair Value
Mortgage-backed securities	469,636
Held to Maturity, Amortized Cost
Mortgage-backed securities	83,897
Held to Maturity, Fair Value
Mortgage-backed securities	$ 83,091