Goodwill and Other Intangible Assets - Schedule of Gross Carrying Amounts and Accumulated Amortization of Other Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 102,623	$ 111,850
Accumulated Amortization and Impairment	(64,946)	(76,542)
Net Carrying Amount	37,677	35,308
Core Deposit [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	81,663	60,103
Accumulated Amortization and Impairment	(53,214)	(43,982)
Net Carrying Amount	28,449	16,121
Customer Business Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount		30,787
Accumulated Amortization and Impairment		(23,341)
Net Carrying Amount		7,446
Customer Trust Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	16,547	16,547
Accumulated Amortization and Impairment	(7,753)	(5,286)
Net Carrying Amount	8,794	11,261
Customer Loan Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	4,413	4,413
Accumulated Amortization and Impairment	(3,979)	(3,933)
Net Carrying Amount	$ 434	$ 480