Loans - Activity in Allowance for Loan Losses by Portfolio Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	$ 104,453	$ 110,147
Provision for loan losses	6,000	1,100
Charge-offs	(19,931)	(8,128)
Recoveries	3,067	4,062
Net charge-offs	(16,864)	(4,066)
Ending balance	93,589	107,181
Loans individually evaluated for impairment	18,040	20,816
Loans collectively evaluated for impairment	75,549	86,365
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	54,164	42,774
Provision for loan losses	13,448	4,766
Charge-offs	(17,152)	(3,012)
Recoveries	625	1,341
Net charge-offs	(16,527)	(1,671)
Ending balance	51,085	45,869
Loans individually evaluated for impairment	13,464	17,842
Loans collectively evaluated for impairment	37,621	28,027
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	29,346	20,912
Provision for loan losses	(4,866)	1,441
Charge-offs	(266)	(2,842)
Recoveries	595	492
Net charge-offs	329	(2,350)
Ending balance	24,809	20,003
Loans individually evaluated for impairment	4,576	2,879
Loans collectively evaluated for impairment	20,233	17,124
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	5,252	3,540
Provision for loan losses	172	(75)
Charge-offs	(336)	(289)
Recoveries	60	523
Net charge-offs	(276)	234
Ending balance	5,148	3,699
Loans individually evaluated for impairment		95
Loans collectively evaluated for impairment	5,148	3,604
Consumer and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	3,507	12,635
Provision for loan losses	607	(3,641)
Charge-offs	(2,177)	(1,985)
Recoveries	1,787	1,706
Net charge-offs	(390)	(279)
Ending balance	3,724	8,715
Loans individually evaluated for impairment
Loans collectively evaluated for impairment	3,724	8,715
Unallocated Financing Receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Beginning balance	12,184	30,286
Provision for loan losses	(3,361)	(1,391)
Charge-offs
Recoveries
Net charge-offs
Ending balance	8,823	28,895
Loans individually evaluated for impairment
Loans collectively evaluated for impairment	$ 8,823	$ 28,895