Condensed Financial Information (Parent Company Only) - Condensed Statements of Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Activities
Net income	$ 6,175	$ 4,288	$ 4,728	$ 5,358	$ 4,948	$ 4,958	$ 4,778	$ 3,417	$ 20,549	$ 18,101	$ 19,876
Items not requiring (providing) cash
Change in Share based compensation									288	203	48
Other assets									8,569	(4,945)	9,905
Other liabilities									(472)	712	498
Net cash provided by operating activities									35,230	17,665	46,965
Investing Activities
Net cash used in investing activities									(124,188)	(149,046)	49,797
Financing Activities
Dividends paid on preferred shares									(125)	(133)	(370)
Dividends paid on common shares									(6,216)	(4,744)	(3,655)
Net cash provided by financing activities									94,132	143,136	(95,776)
Net Change in Cash and Cash Equivalents									5,174	11,755	986
Cash and Cash Equivalents, Beginning of Period				43,476				31,721	43,476	31,721	30,735
Cash and Cash Equivalents, End of Period	48,650				43,476				48,650	43,476	31,721
Summit [Member]
Investing Activities
Acquisition of businesses										7,914
Peoples Bancorp Inc [Member]
Investing Activities
Acquisition of businesses									182,413
Parent Company [Member]
Operating Activities
Net income									20,549	18,101	19,876
Items not requiring (providing) cash
Equity in undistributed net income of subsidiaries									8,168	(6,814)	(13,144)
Change in Share based compensation									288	203	48
Amortization of unearned compensation									355	363	288
Other assets									(634)	906	(167)
Other liabilities									(13)	1,377	97
Net cash provided by operating activities									28,713	14,136	6,998
Investing Activities
Net cash used in investing activities									(19,365)	(7,036)
Financing Activities
Dividends paid on preferred shares									(125)	(133)	(370)
Dividends paid on common shares									(6,216)	(4,744)	(3,655)
Exercise of stock options									4,305	165	195
Net cash provided by financing activities									(2,036)	(4,712)	(3,830)
Net Change in Cash and Cash Equivalents									7,312	2,388	3,168
Cash and Cash Equivalents, Beginning of Period				$ 19,195				$ 16,807	19,195	16,807	13,639
Cash and Cash Equivalents, End of Period	$ 26,507				$ 19,195				26,507	19,195	$ 16,807
Parent Company [Member] | Summit [Member]
Investing Activities
Acquisition of businesses										$ (7,036)
Parent Company [Member] | Peoples Bancorp Inc [Member]
Investing Activities
Acquisition of businesses									$ (19,365)