Loans - Schedule of Legacy Loans on Nonaccrual Status (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	$ 51,274	$ 34,970
Commercial Loans | Commercial Real Estate - Construction
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	180	69
Commercial Loans | Commercial Real Estate - Other
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	14,299	6,859
Commercial Loans | Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	10,776	3,025
Commercial Loans | Energy-Related
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	3,478	27
Residential Mortgage Loans | Residential Mortgage
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	14,879	14,362
Consumer and Other Loans | Consumer - Home Equity
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	5,278	7,404
Consumer and Other Loans | Consumer - Indirect Automobile
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	1,129	1,419
Consumer and Other Loans | Consumer - Credit Card
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	335	1,032
Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Total loans on nonaccrual status	$ 920	$ 773