Loans (Troubled Debt Restructurings) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Modifications [Line Items]
Balance at Restructure	$ 91,418	$ 709	$ 8,916
Balance at Year-end	44,863	536	8,339
Commercial Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Balance at Restructure	2,148	709	5,795
Balance at Year-end	1,022	536	5,391
Commercial and Industrial, Energy [Member]
Financing Receivable, Modifications [Line Items]
Balance at Restructure	87,572	0	0
Balance at Year-end	43,841	0	0
Commercial Real Estate, Buildings, Land and Other [Member]
Financing Receivable, Modifications [Line Items]
Balance at Restructure	1,455	0	3,121
Balance at Year-end	0	0	2,948
Construction Loans [Member]
Financing Receivable, Modifications [Line Items]
Balance at Restructure	243	0	0
Balance at Year-end	$ 0	$ 0	$ 0