Stockholders' Equity (Stock Rollforward) (Details) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Increase (Decrease) in Stock by Class
Common stock, shares issued, beginning of period	18,931,200
Treasury stock, shares, beginning of period	586,688
Changes related to stock-based compensation awards:
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	(1,775)
Changes related to deferred compensation plan:
Purchase of treasury stock	279,770	0
Changes related to private placement:
Common stock, shares issued, end of period	18,939,091	18,931,200
Treasury stock, shares, end of period	795,758	586,688
Common Stock
Class of Stock
Stock Issued During Period, Shares, Restricted Stock Award, Gross		131,011	101,926
Increase (Decrease) in Stock by Class
Common stock, shares issued, beginning of period	18,931,200	15,599,643	11,352,036
Changes related to stock-based compensation awards:
Stock Issued During Period, Shares, Restricted Stock Award, Forfeited	(11,820)	(28,219)	(6,062)
Stock Issued During Period, Shares, Share-based Compensation, Gross		(2,810)	(100)
Changes related to dividend reinvestment plan:
Common shares issued under dividend reinvestment plan	19,711	18,257	17,230
Changes related to private placement:
Common stock, shares issued, end of period	18,939,091	18,931,200	15,599,643
Treasury Stock
Increase (Decrease) in Stock by Class
Treasury stock, shares, beginning of period	586,686	590,246	600,794
Changes related to stock-based compensation awards:
Release of restricted common shares	17,220	25,205	18,031
Stock Issued During Period, Shares, Restricted Stock Award, Forfeited	1,000
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures		(100)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period			(2,792)
Stock Issued During Period, Shares, Share-based Compensation, Gross	(350)
Reissuance of treasury stock for common stock awards			(12,030)
Changes related to deferred compensation plan:
Purchase of treasury stock	8,396	7,654	4,236
Reissuance of treasury stock	(12,012)	(9,642)	(9,390)
Stock Repurchased During Period, Shares	279,770
Changes related to Board Compensation:
Common shares issued under compensation plan for Board of Directors	(11,450)	(10,231)	(8,603)
Stock Issued During Period, Shares, Employee Stock Purchase Plans	(15,727)	(16,446)
Changes related to private placement:
Treasury stock, shares, end of period	795,758	586,686	590,246
Restricted Shares | Treasury Stock
Changes related to stock-based compensation awards:
Stock Issued During Period, Shares, Share-based Compensation, Gross	(56,000)
NB&T Financial Group, Inc. [Member] | Common Stock
Changes related to stock issued in acquisitions:
Stock Issued During Period, Shares, Acquisitions		3,207,698
NB&T Financial Group, Inc. [Member] | Common Stock
Changes related to stock issued in acquisitions:
Stock Issued During Period, Shares, Acquisitions	3,207,698
Midwest Bancshares, Inc. | Common Stock
Changes related to stock issued in acquisitions:
Stock Issued During Period, Shares, Acquisitions			256,282
Ohio Heritage Bancorp, Inc. | Common Stock
Changes related to stock issued in acquisitions:
Stock Issued During Period, Shares, Acquisitions			1,364,735
North Akron Savings Bank | Common Stock
Changes related to stock issued in acquisitions:
Stock Issued During Period, Shares, Acquisitions			665,570
Private Placement [Member] | Common Stock
Changes related to private placement:
Issuance of Private Placement			1,847,826
Private Placement [Member] | Common Stock
Changes related to private placement:
Issuance of Private Placement	1,847,826