Goodwill and Other Intangible Assets - Schedule of Gross Carrying Amounts and Accumulated Amortization of Other Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 135,598	$ 145,647
Accumulated Amortization and Impairment	(75,493)	(68,631)
Net Carrying Amount	60,105	77,016
Core Deposit [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	119,051	129,100
Accumulated Amortization and Impairment	(63,020)	(57,524)
Net Carrying Amount	56,031	71,576
Customer Trust Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	16,547	16,547
Accumulated Amortization and Impairment	(12,473)	(11,107)
Net Carrying Amount	$ 4,074	$ 5,440