Goodwill and Other Intangible Assets - Schedule of Gross Carrying Amount and Accumulated Amortization of Other Intangible Assets (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 80,335	$ 76,735
Accumulated Amortization and Impairment	(53,739)	(47,515)
Net Carrying Amount	26,596	29,220	31,273
Core Deposit [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	44,021	40,559
Accumulated Amortization and Impairment	(29,987)	(25,908)
Net Carrying Amount	14,034	14,651
Customer Business Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	26,549	26,411
Accumulated Amortization and Impairment	(19,444)	(18,153)
Net Carrying Amount	7,105	8,258
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	5,352	5,352
Accumulated Amortization and Impairment	(1,633)	(1,080)
Net Carrying Amount	3,719	4,272
Customer Loan Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	4,413	4,413
Accumulated Amortization and Impairment	(2,675)	(2,374)
Net Carrying Amount	$ 1,738	$ 2,039