Consolidated Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock, par value $2.50	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]
Beginning Balance at Dec. 31, 2018	$ 2,247,573	$ 554,377	$ 1,489,703	$ 946,032	$ (59,063)	$ (683,476)
Beginning Balance (in shares) at Dec. 31, 2018		170,184
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	178,550			178,550
Other comprehensive income	65,144				65,144
Stock issued (in shares)		701
Stock issued	3,813	$ 1,511	1,496			806
Stock-based compensation awards (in shares)
Stock-based compensation awards	5,458		5,458
Acquisition of treasury stock (in shares)		(6,849)
Acquisition of treasury stock (in shares)	(111,457)					(111,457)
Common stock cash dividends	(65,065)			(65,065)
Ending Balance at Sep. 30, 2019	2,324,016	$ 555,888	1,496,657	1,059,517	6,081	(794,127)
Ending Balance (in shares) at Sep. 30, 2019		164,036
Beginning Balance at Jun. 30, 2019	2,308,798	$ 555,690	1,493,628	1,018,736	(12,157)	(747,099)
Beginning Balance (in shares) at Jun. 30, 2019		166,903
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	62,108			62,108
Other comprehensive income	18,238				18,238
Stock issued (in shares)		157
Stock issued	2,160	$ 198	919			1,043
Stock-based compensation awards (in shares)
Stock-based compensation awards	2,110		2,110
Acquisition of treasury stock (in shares)		(3,024)
Acquisition of treasury stock (in shares)	(48,071)					(48,071)
Common stock cash dividends	(21,327)			(21,327)
Ending Balance at Sep. 30, 2019	2,324,016	$ 555,888	1,496,657	1,059,517	6,081	(794,127)
Ending Balance (in shares) at Sep. 30, 2019		164,036
Beginning Balance at Dec. 31, 2019	2,342,176	$ 556,110	1,499,681	1,079,391	(137)	(792,869)
Beginning Balance (in shares) at Dec. 31, 2019		164,218
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	127,213			127,213
Other comprehensive income	57,091				57,091
Stock issued (in shares)		824
Stock issued	5,046	$ 1,608	646			2,792
Stock-based compensation awards (in shares)
Stock-based compensation awards	5,403		5,403
Acquisition of treasury stock (in shares)		(2,908)
Acquisition of treasury stock (in shares)	(39,748)					(39,748)
Common stock cash dividends	(63,113)			(63,113)
Ending Balance at Sep. 30, 2020	2,390,261	$ 557,718	1,505,730	1,099,684	56,954	(829,825)
Ending Balance (in shares) at Sep. 30, 2020		162,134
Beginning Balance at Jun. 30, 2020	2,340,501	$ 557,569	1,503,750	1,059,160	51,439	(831,417)
Beginning Balance (in shares) at Jun. 30, 2020		161,958
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	61,607
Other comprehensive income	5,515				5,515
Stock issued (in shares)		176
Stock issued	1,846	$ 149	105			1,592
Stock-based compensation awards (in shares)
Stock-based compensation awards	1,875		1,875
Common stock cash dividends	(21,083)			(21,083)
Ending Balance at Sep. 30, 2020	$ 2,390,261	$ 557,718	$ 1,505,730	$ 1,099,684	$ 56,954	$ (829,825)
Ending Balance (in shares) at Sep. 30, 2020		162,134