Loans - Net (Charge-Offs)/Recoveries, Segregated by Class of Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	$ (364)	$ (5,361)	$ (6,040)	$ (25,989)
Commercial and industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	2	0	449	(900)
Commercial and industrial, Other commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	738	(4,296)	(2,539)	(22,806)
Commercial real estate, Buildings, land and other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	53	110	(1,965)	81
Commercial real estate, Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	31	16	346	246
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	(609)	(457)	(613)	(718)
Consumer and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	$ (579)	$ (734)	$ (1,718)	$ (1,892)