Intangible Assets and Goodwill - Summary of Intangible Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 38,911	$ 39,247
Accumulated Amortization	(18,997)	(16,639)
Net Carrying Amount	19,914	22,608
Core Deposit Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	35,561	35,856
Accumulated Amortization	(16,366)	(14,131)
Net Carrying Amount	19,195	21,725
Customer Relationship Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	3,350	3,391
Accumulated Amortization	(2,631)	(2,508)
Net Carrying Amount	$ 719	$ 883