Consolidated Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock	Accelerated Stock Repurchase Program	Accelerated Stock Repurchase Program Common Stock	Accelerated Stock Repurchase Program Additional Paid-in Capital	Accelerated Stock Repurchase Program Treasury Stock
Beginning Balance at Dec. 31, 2014	$ 1,996,665	$ 545,555	$ 1,420,523	$ 558,810	$ (17,722)	$ (510,501)
Beginning Balance (in shares) at Dec. 31, 2014		178,924
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	149,502			149,502
Other comprehensive loss	(4,295)				(4,295)
Stock issued, including related tax benefits	10,808	$ 1,586	4,229			4,993
Stock issued, including related tax benefits (in shares)		1,018
Stock-based compensation awards	5,938		5,938
Acquisition of treasury stock	(50,000)					(50,000)
Acquisition of treasury stock (in shares)		(3,976)						(1,790)
Deferred accelerated stock repurchase payment							$ 0		$ 20,000	$ (20,000)
Common stock cash dividends	(66,724)			(66,724)
Ending Balance at Dec. 31, 2015	2,041,894	$ 547,141	1,450,690	641,588	(22,017)	(575,508)
Ending Balance (in shares) at Dec. 31, 2015		174,176
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	161,625			161,625
Other comprehensive loss	(16,432)				(16,432)
Stock issued, including related tax benefits	17,131	$ 2,566	10,356			4,209
Stock issued, including related tax benefits (in shares)		1,350
Stock-based compensation awards	6,556		6,556
Acquisition of treasury stock	(18,545)					(18,545)
Acquisition of treasury stock (in shares)		(1,486)
Common stock cash dividends	(71,114)			(71,114)
Ending Balance at Dec. 31, 2016	2,121,115	$ 549,707	1,467,602	732,099	(38,449)	(589,844)
Ending Balance (in shares) at Dec. 31, 2016		174,040
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	171,753			171,753
Other comprehensive loss	5,475				5,475
Stock issued, including related tax benefits	8,538	$ 2,525	5,578			435
Stock issued, including related tax benefits (in shares)		1,130
Stock-based compensation awards	5,209		5,209
Common stock cash dividends	(82,233)			(82,233)
Ending Balance at Dec. 31, 2017	$ 2,229,857	$ 552,232	$ 1,478,389	$ 821,619	$ (32,974)	$ (589,409)
Ending Balance (in shares) at Dec. 31, 2017		175,170