Goodwill and Other Intangible Assets - Schedule of Gross Carrying Amount and Accumulated Amortization of Other Intangible Assets (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 81,634	$ 81,634
Accumulated Amortization and Impairment	(57,514)	(55,677)
Net Carrying Amount	24,120	25,957	26,695
Core deposit intangible [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	44,021	44,021
Accumulated Amortization and Impairment	(32,426)	(31,266)
Net Carrying Amount	11,595	12,755
Customer Business Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	27,848	27,848
Accumulated Amortization and Impairment	(20,233)	(19,826)
Net Carrying Amount	7,615	8,022
Trust customer relationship intangible [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	5,352	5,352
Accumulated Amortization and Impairment	(1,980)	(1,810)
Net Carrying Amount	3,372	3,542
Customer Loan Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	4,413	4,413
Accumulated Amortization and Impairment	(2,875)	(2,775)
Net Carrying Amount	$ 1,538	$ 1,638