Stockholders' Equity (Narrative) (Details) - USD ($) $ in Thousands		12 Months Ended
	Feb. 27, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jan. 28, 2021
Class of Stock
Issuance of common shares related to acquisition of NB&T Financial Group, Inc.			$ 32,437	$ 40,898
Stock Repurchase Program, Authorized Amount	$ 40,000		$ 20,000
Purchase of treasury stock				0
Preferred stock, shares authorized		50,000	50,000
Preferred stock, shares issued		0	0
Payments for Repurchase of Common Stock		$ 29,281	$ 805	$ 0
Subsequent Event
Class of Stock
Stock Repurchase Program, Authorized Amount					$ 30,000
Common Stock
Class of Stock
Common shares issued under dividend reinvestment plan		37,259	26,287	19,282
Treasury Stock
Class of Stock
Purchase of treasury stock		12,005	7,227	6,526
Stock Repurchased During Period, Shares	6,300,000	1,299,577	26,427
Payments for Repurchase of Common Stock		$ 29,300
Treasury Stock | Share Repurchase Program Authorized in November 2015
Class of Stock
Payments for Repurchase of Common Stock		843
Treasury Stock | Share Repurchase Program Authorized in February 2020
Class of Stock
Payments for Repurchase of Common Stock		$ 28,500