Goodwill and Other Intangible Assets - Schedule of Gross Carrying Amounts and Accumulated Amortization of Other Intangible Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 102,623	$ 102,623
Accumulated Amortization and Impairment	(70,747)	(64,946)
Net Carrying Amount	31,876	37,677	$ 44,237
Core Deposit [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	81,663	81,663
Accumulated Amortization and Impairment	(57,906)	(53,214)
Net Carrying Amount	23,757	28,449
Customer Trust Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	16,547	16,547
Accumulated Amortization and Impairment	(8,662)	(7,753)
Net Carrying Amount	7,885	8,794
Customer Loan Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	4,413	4,413
Accumulated Amortization and Impairment	(4,179)	(3,979)
Net Carrying Amount	$ 234	$ 434