Securities - Summary of Contractual Maturities of Investment Securities Classified as Available for Sale and Held to Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Available for Sale, Amortized Cost
Due in one year or less	$ 13,410
Due after one year through five years	62,626
Due after five years through ten years	53,139
Due after ten years	198,539
Total	327,714
Mortgage-backed and asset-backed securities	511,558
Amortized Cost	839,272	$ 752,260
Available for Sale, Fair Value
Due in one year or less	13,603
Due after one year through five years	64,509
Due after five years through ten years	54,782
Due after ten years	201,489
Total	334,383
Mortgage-backed and asset-backed securities	521,363
Investment securities, available for sale, at fair value	855,746	755,900
Held to Maturity, Amortized Cost
Due in one year or less	9,022
Due after one year through five years	21,535
Due after five years through ten years	3,130
Due after ten years	2,508
Total	36,195
Mortgage-backed and asset-backed securities	54,571
Amortized Cost	90,766	123,975
Held to Maturity, Fair Value
Due in one year or less	9,078
Due after one year through five years	22,440
Due after five years through ten years	3,193
Due after ten years	2,543
Total	37,254
Mortgage-backed and asset-backed securities	56,614
Total securities, Held to Maturity, Fair Value	$ 93,868	$ 124,904