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, 2013	Dec. 31, 2012	Jun. 30, 2012
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 76,873	$ 76,735
Accumulated Amortization and Impairment	(51,880)	(47,515)
Net Carrying Amount	24,993	29,220	30,205
Core Deposits [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	40,559	40,559
Accumulated Amortization and Impairment	(28,772)	(25,908)
Net Carrying Amount	11,787	14,651
Customer Business Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	26,549	26,411
Accumulated Amortization and Impairment	(19,081)	(18,153)
Net Carrying Amount	7,468	8,258
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	5,352	5,352
Accumulated Amortization and Impairment	(1,453)	(1,080)
Net Carrying Amount	3,899	4,272
Customer Loan Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	4,413	4,413
Accumulated Amortization and Impairment	(2,574)	(2,374)
Net Carrying Amount	$ 1,839	$ 2,039