Consolidated Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands		Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	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		84,677			84,677
Other comprehensive income		(33,183)				(33,183)
Stock issued (in shares)			661
Stock issued		2,455	$ 1,686	1,652			(883)
Stock-based compensation awards (in shares)			16
Stock-based compensation awards		4,184	$ 40	4,144
Reclassification of stranded tax effects	[1]				7,101	(7,101)
Common stock cash dividends		(42,205)			(42,205)
Ending Balance at Jun. 30, 2018		2,245,785	$ 553,958	1,484,185	871,192	(73,258)	(590,292)
Ending Balance (in shares) at Jun. 30, 2018			175,847
Beginning Balance at Mar. 31, 2018		2,235,493	$ 552,682	1,481,545	857,153	(67,172)	(588,715)
Beginning Balance (in shares) at Mar. 31, 2018			175,404
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income		35,197			35,197
Other comprehensive income		(6,086)				(6,086)
Stock issued (in shares)			427
Stock issued		(335)	$ 1,236	6			(1,577)
Stock-based compensation awards (in shares)			16
Stock-based compensation awards		2,674	$ 40	2,634
Common stock cash dividends		(21,158)			(21,158)
Ending Balance at Jun. 30, 2018		2,245,785	$ 553,958	1,484,185	871,192	(73,258)	(590,292)
Ending Balance (in shares) at Jun. 30, 2018			175,847
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		116,442
Other comprehensive income		46,906				46,906
Stock issued (in shares)			544
Stock issued		1,653	$ 1,313	577			(237)
Stock-based compensation awards (in shares)
Stock-based compensation awards		3,348		3,348
Acquisition of treasury stock (in shares)			(3,825)
Acquisition of treasury stock (in shares)		(63,386)					(63,386)
Common stock cash dividends		(43,738)			(43,738)
Ending Balance at Jun. 30, 2019		2,308,798	$ 555,690	1,493,628	1,018,736	(12,157)	(747,099)
Ending Balance (in shares) at Jun. 30, 2019			166,903
Beginning Balance at Mar. 31, 2019		2,301,019	$ 554,485	1,491,870	980,708	(37,633)	(688,411)
Beginning Balance (in shares) at Mar. 31, 2019			169,923
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income		59,779
Other comprehensive income		25,476				25,476
Stock issued (in shares)			429
Stock issued		(4)	$ 1,205	(30)			(1,179)
Stock-based compensation awards (in shares)
Stock-based compensation awards		1,788		1,788
Acquisition of treasury stock (in shares)			(3,449)
Acquisition of treasury stock (in shares)		(57,509)					(57,509)
Common stock cash dividends		(21,751)			(21,751)
Ending Balance at Jun. 30, 2019		$ 2,308,798	$ 555,690	$ 1,493,628	$ 1,018,736	$ (12,157)	$ (747,099)
Ending Balance (in shares) at Jun. 30, 2019			166,903

[1] (1) The Corporation adopted the Accounting Standards Codification ("ASC") Update 2018-02, "Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income" in the first quarter of 2018 which permitted a reclassification from accumulated other comprehensive income ("AOCI") to retained earnings of the stranded tax effects resulting from the Tax Cuts and Jobs Act of 2017, which changed the federal corporate income tax rate from 35% to 21%. As a result, $7.1 million of stranded tax effects were reclassified from AOCI to retained earnings during the first quarter of 2018.