Loans - Net (Charge-Offs)/Recoveries, Segregated by Class of Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	$ (16,864)	$ (4,066)
Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs		4
Commercial and Industrial, Other Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	(16,527)	(1,675)
Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	215	(2,360)
Commercial Real Estate, Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	114	10
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	(276)	234
Consumer and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	$ (390)	$ (279)