Loans - Net (Charge-Offs)/Recoveries, Segregated by Class of Loans (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
(Net charge-offs)/Recoveries	$ (6,785)	$ (12,424)
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
(Net charge-offs)/Recoveries	(1,938)	(7,675)
Commercial and industrial, Energy [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
(Net charge-offs)/Recoveries	47	(2,849)
Commercial real estate, Buildings, land and other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
(Net charge-offs)/Recoveries	27	81
Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
(Net charge-offs)/Recoveries	3	2
Consumer Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
(Net charge-offs)/Recoveries	(1,689)	(526)
Consumer and Other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
(Net charge-offs)/Recoveries	$ (3,235)	$ (1,457)