Stockholders' Equity (Stock Rollforward) (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Increase (Decrease) in Stock by Class
Common stock, shares issued, beginning of period	18,939,091
Treasury stock, shares, beginning of period	795,758
Changes related to deferred compensation plan:
Purchase of treasury stock	0	279,770	0
Changes related to stock issued in acquisitions:
Common stock, shares issued, end of period	18,952,385	18,939,091
Treasury stock, shares, end of period	702,449	795,758
Common Stock
Increase (Decrease) in Stock by Class
Common stock, shares issued, beginning of period	18,939,091	18,931,200	15,599,643
Changes related to stock-based compensation awards:
Stock Issued During Period, Shares, Restricted Stock Award, Gross		0	131,011
Stock Issued During Period, Shares, Restricted Stock Award, Forfeited	(3,554)	(11,820)	28,219
Stock Issued During Period, Shares, Share-based Compensation, Gross		0	(2,810)
Changes related to dividend reinvestment plan:
Common shares issued under dividend reinvestment plan	16,848	19,711	18,257
Changes related to stock issued in acquisitions:
Common stock, shares issued, end of period	18,952,385	18,939,091	18,931,200
Treasury Stock
Increase (Decrease) in Stock by Class
Treasury stock, shares, beginning of period	795,758	586,686	590,246
Changes related to stock-based compensation awards:
Stock Issued During Period, Shares, Restricted Stock Award, Gross	(68,707)	(56,000)
Release of restricted common shares	10,452	17,220	25,205
Stock Issued During Period, Shares, Restricted Stock Award, Forfeited	5,050	1,000
Stock Issued During Period, Shares, Share-based Compensation, Gross			100
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures	(300)	(350)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	(266)	(1,775)
Changes related to deferred compensation plan:
Purchase of treasury stock	5,413	8,396	7,654
Reissuance of treasury stock	(24,634)	(12,012)	(9,642)
Stock Repurchased During Period, Shares		279,770
Changes related to Board Compensation:
Common shares issued under compensation plan for Board of Directors	9,092	11,450	10,231
Stock Issued During Period, Shares, Employee Stock Purchase Plans	(11,225)	(15,727)	(16,446)
Changes related to stock issued in acquisitions:
Treasury stock, shares, end of period	702,449	795,758	586,686
NB&T Financial Group, Inc. | Common Stock
Changes related to stock issued in acquisitions:
Stock Issued During Period, Shares, Acquisitions			3,207,698
NB&T Financial Group, Inc. | Common Stock
Changes related to stock issued in acquisitions:
Stock Issued During Period, Shares, Acquisitions	3,207,698