Consolidated Statements of Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Capital Surplus	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Treasury Stock
Balance at Beginning of Period at Dec. 31, 2018	$ 1,268,200	$ 577	$ 571,704	$ (51,043)	$ 1,641,314	$ (894,352)
Beginning Balance (in shares) at Dec. 31, 2018		41,499,898
Increase (decrease) in shareholders' equity
Net Income	58,799				58,799
Other Comprehensive Income	7,165			7,165
Share-Based Compensation	2,274		2,274
Common Stock Issued under Purchase and Equity Compensation Plans	2,087	$ 1	616		(203)	1,673
Common Stock Issued under Purchase and Equity Compensation Plans and Related Tax Benefits (in shares)		131,529
Common Stock Repurchased	(43,189)					(43,189)
Common Stock Repurchased (in shares)		(552,739)
Cash Dividends Declared (per share)	(25,646)				(25,646)
Balance at End of Period at Mar. 31, 2019	1,269,690	$ 578	574,594	(43,878)	1,674,264	(935,868)
Ending Balance (in shares) at Mar. 31, 2019		41,078,688
Balance at Beginning of Period at Dec. 31, 2019	$ 1,286,832	$ 579	582,566	(31,112)	1,761,415	(1,026,616)
Beginning Balance (in shares) at Dec. 31, 2019	40,039,695	40,039,695
Increase (decrease) in shareholders' equity
Net Income	$ 34,742				34,742
Other Comprehensive Income	41,933			41,933
Share-Based Compensation	1,497		1,497
Common Stock Issued under Purchase and Equity Compensation Plans	3,761	$ 0	329		653	2,779
Common Stock Issued under Purchase and Equity Compensation Plans and Related Tax Benefits (in shares)		154,091
Common Stock Repurchased	(17,633)					(17,633)
Common Stock Repurchased (in shares)		(197,276)
Cash Dividends Declared (per share)	(26,835)				(26,835)
Balance at End of Period at Mar. 31, 2020	$ 1,327,929	$ 579	$ 584,392	$ 10,821	$ 1,773,607	$ (1,041,470)
Ending Balance (in shares) at Mar. 31, 2020	39,996,510	39,996,510