Investment Securities - Summary of Contractual Maturities of Investment Securities Classified as Available for Sale and Held to Maturity (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Available for Sale, Amortized Cost
Due in one year or less	$ 25,763
Due after one year through five years	44,924
Due after five years through ten years	78,833
Due after ten years	253,034
Total	402,554
Total securities	981,126
Available for Sale, Fair Value
Due in one year or less	26,042
Due after one year through five years	46,127
Due after five years through ten years	80,737
Due after ten years	253,958
Total	406,864
Total securities	988,673
Held to Maturity, Amortized Cost
Due in one year or less	7,809
Due after one year through five years	15,940
Due after five years through ten years	7,493
Due after ten years	8,358
Total	39,600
Amortized Cost	94,415
Held to Maturity, Fair Value
Due in one year or less	7,913
Due after one year through five years	16,489
Due after five years through ten years	7,444
Due after ten years	8,406
Total	40,252
Total securities	96,174	$ 93,868
Mortgage-backed and asset-backed securities
Available for Sale, Amortized Cost
Mortgage-backed and asset-backed securities	578,572
Available for Sale, Fair Value
Mortgage-backed and asset-backed securities	581,809
Held to Maturity, Amortized Cost
Mortgage-backed and asset-backed securities	54,815
Held to Maturity, Fair Value
Mortgage-backed and asset-backed securities	$ 55,922