Loans - Troubled Debt Restructurings (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	$ 64,755	$ 709
Balance at period end	22,980	584
Commercial Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	510	709
Balance at period end	505	584
Commercial and industrial, Energy [Member]
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	62,546	0
Balance at period end	20,795	0
Commercial real estate, Buildings, land and other [Member]
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	1,456	0
Balance at period end	1,456	0
Construction Loans [Member]
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	243	0
Balance at period end	$ 224	$ 0