Loans (Troubled Debt Restructurings) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable, Modifications [Line Items]
Balance at Restructure	$ 8,916	$ 14,833	$ 2,316
Balance at Year-end	8,339	11,215	2,188
Commercial and Industrial, Energy [Member]
Financing Receivable, Modifications [Line Items]
Balance at Restructure	0	528	0
Balance at Year-end	0	531	0
Commercial and Industrial, Other Commercial [Member]
Financing Receivable, Modifications [Line Items]
Balance at Restructure	5,795	6,334	1,602
Balance at Year-end	5,391	4,937	1,478
Commercial Real Estate, Buildings, Land and Other [Member]
Financing Receivable, Modifications [Line Items]
Balance at Restructure	3,121	7,964	714
Balance at Year-end	2,948	5,747	710
Consumer Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Balance at Restructure	0	0	0
Balance at Year-end	0	0	0
Consumer [Member]
Financing Receivable, Modifications [Line Items]
Balance at Restructure	0	7	0
Balance at Year-end	$ 0	$ 0	$ 0