Accounting for Certain Loans Acquired in a Transfer - Accretable Yield or Income Expected to be Collected (Detail) - Loans Purchased With Evidence Of Credit Deterioration [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at January 1	$ 3,668	$ 3,185
Additions	647	1,688
Accretion	(725)	(889)
Reclassification from nonaccretable difference	0	0
Disposals	(1,532)	(316)
Balance at December 31	2,058	3,668
Heartland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at January 1	2,400	3,185
Accretion	(327)	(557)
Reclassification from nonaccretable difference	0	0
Disposals	(1,278)	(228)
Balance at December 31	795	2,400
Summit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at January 1	1,268
Additions		1,688
Accretion	(315)	(332)
Reclassification from nonaccretable difference	0	0
Disposals	(245)	(88)
Balance at December 31	708	1,268
Peoples Bancorp Inc [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Additions	647
Accretion	(83)
Reclassification from nonaccretable difference	0	$ 0
Disposals	(9)
Balance at December 31	$ 555