Investment Securities - Summary of Contractual Maturities of Investment Securities Classified as Available for Sale and Held to Maturity (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Available for Sale, Amortized Cost
Due in one year or less	$ 20,779
Due after one year through five years	53,784
Due after five years through ten years	63,139
Due after ten years	250,401
Total	388,103
Total securities	970,699	$ 839,272
Available for Sale, Fair Value
Due in one year or less	21,049
Due after one year through five years	55,207
Due after five years through ten years	64,336
Due after ten years	243,115
Total	383,707
Total securities	968,394	855,746
Held to Maturity, Amortized Cost
Due in one year or less	9,425
Due after one year through five years	20,950
Due after five years through ten years	3,017
Due after ten years	2,507
Total	35,899
Amortized Cost	84,994	90,766
Held to Maturity, Fair Value
Due in one year or less	9,450
Due after one year through five years	21,673
Due after five years through ten years	3,068
Due after ten years	2,553
Total	36,744
Total securities	87,215	$ 93,868
Mortgage-backed and asset-backed securities
Available for Sale, Amortized Cost
Mortgage-backed and asset-backed securities	582,596
Available for Sale, Fair Value
Mortgage-backed and asset-backed securities	584,687
Held to Maturity, Amortized Cost
Mortgage-backed and asset-backed securities	49,095
Held to Maturity, Fair Value
Mortgage-backed and asset-backed securities	$ 50,471