Loans - Schedule of Legacy Loans on Nonaccrual Status (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	$ 95,096	$ 50,928
Commercial Loans | Commercial Real Estate - Construction
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	26	120
Commercial Loans | Commercial Real Estate - Other
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	3,649	15,422
Commercial Loans | Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	9,616	6,659
Commercial Loans | Energy-Related
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	60,766	7,081
Residential Mortgage Loans | Residential Mortgage
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	12,823	13,674
Consumer - Other | Consumer - Home Equity
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	5,591	5,628
Consumer - Other | Consumer - Indirect Automobile
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	1,372	1,181
Consumer - Other | Consumer - Credit Card
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	532	394
Consumer - Other | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	$ 721	$ 769