Loans - Troubled Debt Restructurings (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	$ 62,808	$ 709
Balance at period end	61,347	613
Commercial Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	19	709
Balance at period end	17	613
Commercial and industrial, Energy [Member]
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	62,546	0
Balance at period end	61,095	0
Construction Loans [Member]
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	243	0
Balance at period end	$ 235	$ 0