Goodwill and Other Intangible Assets - Schedule of Gross Carrying Amounts and Accumulated Amortization of Other Intangible Assets (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 102,623	$ 102,623
Accumulated Amortization and Impairment	(67,966)	(64,946)
Net Carrying Amount	34,657	37,677	$ 32,443
Core Deposit [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	81,663	81,663
Accumulated Amortization and Impairment	(55,671)	(53,214)
Net Carrying Amount	25,992	28,449
Customer Trust Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	16,547	16,547
Accumulated Amortization and Impairment	(8,216)	(7,753)
Net Carrying Amount	8,331	8,794
Customer Loan Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	4,413	4,413
Accumulated Amortization and Impairment	(4,079)	(3,979)
Net Carrying Amount	$ 334	$ 434