Stockholders' Equity (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Class of Stock
Stock Repurchase Program, Authorized Amount	$ 20,000
Purchase of treasury stock	0	279,770	0
Purchase of treasury stock	$ 5,000	$ 4,965
Preferred stock, shares authorized	50,000	50,000
Preferred stock, shares issued	0	0
NB&T Financial Group, Inc.
Class of Stock
Issuance of common shares related to acquisition of NB&T Financial Group, Inc.			$ 76,027
NB&T Financial Group, Inc. | Common Stock
Class of Stock
Stock Issued During Period, Shares, Acquisitions	3,207,698
Issuance of common shares related to acquisition of NB&T Financial Group, Inc.	$ 76,000		$ 76,027