Loans - Troubled Debt Restructurings (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	$ 8,024	$ 15,911
Balance at period end	7,863	843
Commercial Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	677	2,203
Balance at period end	555	843
Commercial and industrial, Energy [Member]
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	0	13,708
Balance at period end	0	0
Commercial real estate, Buildings, land and other [Member]
Financing Receivable, Modifications [Line Items]
Balance at time of restructuring	7,347	0
Balance at period end	$ 7,308	$ 0