Consolidated Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Total	Treasury Stock [Member]
Beginning Balance at Dec. 31, 2017	$ 2,229,857	$ 552,232	$ 1,478,389	$ 821,619	$ (32,974)	$ (589,409)
Beginning Balance (in shares) at Dec. 31, 2017		175,170
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	49,480			49,480
Other comprehensive income	(27,097)				(27,097)
Stock issued, including related tax benefits (in shares)		234
Stock issued	2,790	$ 450	1,646			694
Stock-based compensation awards	1,510		1,510
Reclassification of stranded tax effects	0			7,101	(7,101)
Common stock cash dividends	(21,047)			(21,047)
Ending Balance at Mar. 31, 2018	2,235,493	$ 552,682	1,481,545	857,153	(67,172)	(588,715)
Ending Balance (in shares) at Mar. 31, 2018		175,404
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	56,663
Other comprehensive income	21,430				21,430
Stock issued, including related tax benefits (in shares)		115
Stock issued	1,657	$ 108	607			942
Stock-based compensation awards (in shares)
Stock-based compensation awards	1,560		1,560
Acquisition of treasury stock (in shares)	(5,877)					(5,877)
Common stock cash dividends	(21,987)			(21,987)
Ending Balance at Mar. 31, 2019	$ 2,301,019	$ 554,485	$ 1,491,870	$ 980,708	$ (37,633)	$ (688,411)
Ending Balance (in shares) at Mar. 31, 2019		169,923
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury Stock, Shares, Acquired		376