Loans (Net (Charge-Offs)/Recoveries, Segregated by Class of Loans) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	$ (34,487)	$ (15,528)	$ (9,210)
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	(12,259)	(6,535)	(2,911)
Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	(18,588)	(5,997)	(1,237)
Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	813	314	(2,348)
Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	23	18	348
Residential Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	(257)	(91)	(733)
Consumer Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	$ (4,219)	$ (3,237)	$ (2,329)