Goodwill and Other Intangible Assets - Schedule of Gross Carrying Amount and Accumulated Amortization of Other Intangible Assets (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 90,315	$ 81,634
Accumulated Amortization and Impairment	(59,516)	(55,677)
Net Carrying Amount	30,799	25,957	24,993
Core deposit intangible [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	48,618	44,021
Accumulated Amortization and Impairment	(33,650)	(31,266)
Net Carrying Amount	14,968	12,755
Customer Business Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	28,148	27,848
Accumulated Amortization and Impairment	(20,646)	(19,826)
Net Carrying Amount	7,502	8,022
Trust customer relationship intangible [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	9,136	5,352
Accumulated Amortization and Impairment	(2,245)	(1,810)
Net Carrying Amount	6,891	3,542
Customer Loan Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	4,413	4,413
Accumulated Amortization and Impairment	(2,975)	(2,775)
Net Carrying Amount	$ 1,438	$ 1,638