Loans - Troubled Debt Restructurings (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	$ 13,833	$ 445
Commercial and industrial, Energy [Member]
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	528	0
Commercial and industrial, Other commercial [Member]
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	5,862	445
Commercial real estate, Buildings, land and other [Member]
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	$ 7,443	$ 0