Goodwill and Other Intangible Assets - Schedule of Definite-Lived Intangible Assets (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 122,831	$ 137,774
Accumulated Amortization	(72,217)	(82,974)
Net Carrying Amount	50,614	54,800
Core deposit intangible assets
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	121,277	136,183
Accumulated Amortization	(70,758)	(81,493)
Net Carrying Amount	50,519	54,690
Customer relationship intangible asset
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,348	1,385
Accumulated Amortization	(1,341)	(1,371)
Net Carrying Amount	7	14
Non-compete agreement
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	206	206
Accumulated Amortization	(118)	(110)
Net Carrying Amount	$ 88	$ 96