Acquisition - Pro Forma Result of Comparable Prior Reporting Period (Detail) - Peoples Bancorp Inc [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Net Interest Income	$ 80,688	$ 75,442
Provision for Loan Losses	3,222	3,443
Net Interest Income after Provision for Loan Losses	77,466	71,999
Non-interest Income	32,295	29,928
Non-Interest Expense	80,489	74,010
Income before Income Taxes	29,272	27,917
Income Tax Expense	7,359	6,560
Net Income	21,913	21,357
Net Income Available to Common Shareholders	$ 21,788	$ 21,372
Basic Earnings Per Share	$ 1.90	$ 1.87
Diluted Earnings Per Share	$ 1.85	$ 1.81