Loans (Net (Charge-Offs)/Recoveries, Segregated by Class of Loans) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	$ (44,845)	$ (33,141)	$ (34,487)
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	(22,388)	(17,453)	(12,259)
Commercial and Industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	(13,121)	(10,009)	(18,588)
Commercial Real Estate, Buildings, Land and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	(263)	735	813
Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	13	11	23
Residential Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	(1,538)	(506)	(257)
Consumer Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net charge-offs	$ (7,548)	$ (5,919)	$ (4,219)