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		150,310			150,310
Other comprehensive income		(44,565)				(44,565)
Stock issued (in shares)			833
Stock issued		4,748	$ 1,936	2,773			39
Stock-based compensation awards (in shares)			16
Stock-based compensation awards		6,007	$ 40	5,967
Reclassification of stranded tax effects	[1]				7,101	(7,101)
Common stock cash dividends		(63,343)			(63,343)
Ending Balance at Sep. 30, 2018		2,283,014	$ 554,208	1,487,129	915,687	(84,640)	(589,370)
Ending Balance (in shares) at Sep. 30, 2018			176,019
Beginning Balance at Jun. 30, 2018		2,245,785	$ 553,958	1,484,185	871,192	(73,258)	(590,292)
Beginning Balance (in shares) at Jun. 30, 2018			175,847
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income		65,633			65,633
Other comprehensive income		(11,382)				(11,382)
Stock issued (in shares)			147
Stock issued		2,231	$ 188	1,121			922
Stock-based compensation awards (in shares)			25
Stock-based compensation awards		1,885	$ 62	1,823
Common stock cash dividends		(21,138)			(21,138)
Ending Balance at Sep. 30, 2018		2,283,014	$ 554,208	1,487,129	915,687	(84,640)	(589,370)
Ending Balance (in shares) at Sep. 30, 2018			176,019
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
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
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

[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.