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	9 Months Ended
Sep. 30, 2015	Sep. 30, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at January 1	$ 3,668	$ 3,185
Additions	647	1,758
Accretion	(526)	(288)
Reclassification from nonaccretable difference	0	0
Disposals	(1,447)	(95)
Balance at September 30	2,342	4,560
Heartland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at January 1	2,400	3,185
Accretion	(272)	(288)
Reclassification from nonaccretable difference	0	0
Disposals	(1,210)	(95)
Balance at September 30	918	2,802
Summit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at January 1	1,268
Additions		1,758
Accretion	(254)
Reclassification from nonaccretable difference	0	0
Disposals	(237)
Balance at September 30	777	1,758
Peoples Bancorp Inc [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Additions	647
Reclassification from nonaccretable difference	0	$ 0
Balance at September 30	$ 647

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

9 Months Ended

Sep. 30, 2015

Sep. 30, 2014

Accounts, Notes, Loans and Financing Receivable [Line Items]

Balance at January 1

$ 3,668

$ 3,185

Additions

647

1,758

Accretion

(526)