Loans - Troubled Debt Restructurings (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	$ 76,185	$ 709
Balance at period end	34,099	554
Commercial Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	510	709
Balance at period end	505	554
Commercial and industrial, Energy [Member]
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	73,977	0
Balance at period end	31,918	0
Commercial real estate, Buildings, land and other [Member]
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	1,455	0
Balance at period end	1,455	0
Construction Loans [Member]
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	243	0
Balance at period end	$ 221	$ 0