Loans (Troubled Debt Restructurings) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Modifications [Line Items]
Balance at Restructure	$ 15,911	$ 60,510	$ 91,418
Balance at Year-end	0	58,484	44,863
Commercial Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Balance at Restructure	2,203	4,026	2,148
Balance at Year-end	0	3,766	1,022
Commercial and Industrial, Energy [Member]
Financing Receivable, Modifications [Line Items]
Balance at Restructure	13,708	56,096	87,572
Balance at Year-end	0	54,330	43,841
Commercial Real Estate, Buildings, Land and Other [Member]
Financing Receivable, Modifications [Line Items]
Balance at Restructure	0	0	1,455
Balance at Year-end	0	0	0
Construction Loans [Member]
Financing Receivable, Modifications [Line Items]
Balance at Restructure	0	388	243
Balance at Year-end	$ 0	$ 388	$ 0