Acquisitions (Details) - Acquisition Activity - USD ($) $ / shares in Units, $ in Thousands	Mar. 08, 2016	Dec. 03, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Assets
Goodwill			$ 340,879	$ 319,007	$ 310,589	$ 264,062
Liabilities
Intangible liabilities			$ 8,093
NI Bancshares Corporation
Assets
Cash and due from banks and interest-bearing deposits in other banks	$ 72,533
Securities available-for-sale	125,843
Securities held-to-maturity	1,864
FHLB and FRB stock	1,549
Loans	396,886
OREO	2,863
Investment in BOLI	8,384
Goodwill	21,751
Other intangible assets	10,409
Premises, furniture, and equipment	19,636
Accrued interest receivable and other assets	16,558
Total assets	678,276
Liabilities
Noninterest-bearing deposits	130,909
Interest-bearing deposits	464,012
Total deposits	594,921
Borrowed funds	2,416
Intangible liabilities	230
Accrued interest payable and other liabilities	10,627
Total liabilities	$ 608,194
Consideration Paid
Common stock, shares issued (in shares)	3,042,494
Shares issued (in dollars per share)	$ 18.059
Issuance costs	$ 48
Common stock (2016 - 3,042,494 shares issued at $18.059 per share), net of $48,000 in issuance costs	54,896
Cash paid	15,186
Total consideration paid	$ 70,082
Peoples Bancorp, Inc.
Assets
Cash and due from banks and interest-bearing deposits in other banks		$ 781
Securities available-for-sale		41,492
Securities held-to-maturity		0
FHLB and FRB stock		558
Loans		53,766
OREO		515
Investment in BOLI		0
Goodwill		7,665
Other intangible assets		580
Premises, furniture, and equipment		2,215
Accrued interest receivable and other assets		2,941
Total assets		110,513
Liabilities
Noninterest-bearing deposits		15,869
Interest-bearing deposits		75,944
Total deposits		91,813
Borrowed funds		1,200
Intangible liabilities		0
Accrued interest payable and other liabilities		672
Total liabilities		93,685
Consideration Paid
Common stock (2016 - 3,042,494 shares issued at $18.059 per share), net of $48,000 in issuance costs		0
Total consideration paid		$ 16,828