Loans - Schedule of Legacy Loans on Nonaccrual Status (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	$ 93,429	$ 50,928
Commercial Loans | Commercial Real Estate - Construction
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	42	120
Commercial Loans | Commercial Real Estate - Other
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	13,665	15,422
Commercial Loans | Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	12,538	6,659
Commercial Loans | Energy-Related
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	46,151	7,081
Residential Mortgage Loans | Residential Mortgage
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	12,953	13,674
Consumer - Other | Consumer - Home Equity
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	5,739	5,628
Consumer - Other | Consumer - Indirect Automobile
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	1,145	1,181
Consumer - Other | Consumer - Credit Card
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	468	394
Consumer - Other | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	$ 728	$ 769