Loans - Troubled Debt Restructurings (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	$ 6,874	$ 13,833
Balance at period end	6,524	12,604
Commercial and industrial, Energy [Member]
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	0	528
Balance at period end	0	537
Commercial and industrial, Other commercial [Member]
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	3,752	5,862
Balance at period end	3,516	5,067
Commercial real estate, Buildings, land and other [Member]
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	3,122	7,443
Balance at period end	$ 3,008	$ 7,000