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	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at January 1	$ 2,058	$ 3,668
Additions	0	0
Accretion	(133)	(206)
Reclassification from nonaccretable difference	0	0
Disposals	(44)	(137)
Balance at March 31	1,881	3,325
Heartland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at January 1	795	2,400
Additions	0	0
Accretion	(36)	(107)
Reclassification from nonaccretable difference	0	0
Disposals	(10)	(88)
Balance at March 31	749	2,205
Summit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at January 1	708	1,268
Additions	0	0
Accretion	(55)	(99)
Reclassification from nonaccretable difference	0	0
Disposals	(4)	(49)
Balance at March 31	649	1,120
Peoples Bancorp Inc [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at January 1	555
Additions	0	0
Accretion	(42)
Reclassification from nonaccretable difference	0	$ 0
Disposals	(30)
Balance at March 31	$ 483