Consolidated Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Treasury Stock	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning Balance (in shares) at Dec. 31, 2014		(18,264)
Beginning Balance at Dec. 31, 2014	$ 1,223,521	$ (323,288)	$ 45,376	$ 227,290	$ 1,274,233	$ (90)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends	(6,822)				(6,822)
Stock-Based Compensation (in shares)		5
Stock-Based Compensation	13,694	$ 89		13,605
Reissued Shares (in shares)		107
Reissued Shares	943	$ 1,726		(783)
Net Earnings	135,709				135,709
Foreign Currency Translation Adjustment	(427)					(427)
Ending Balance (in shares) at Dec. 31, 2015		(18,152)
Ending Balance at Dec. 31, 2015	1,366,618	$ (321,473)	45,376	240,112	1,403,120	(517)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends	(7,420)				(7,420)
Stock-Based Compensation (in shares)		4
Stock-Based Compensation	20,228	$ 68		20,160
Reissued Shares (in shares)		217
Reissued Shares	(2,572)	$ 3,188		(5,760)
Net Earnings	139,283				139,283
Foreign Currency Translation Adjustment	(14)					(14)
Repurchased Shares (in shares)		(1,373)
Repurchased Shares	(34,525)	$ (34,525)		0
Ending Balance (in shares) at Dec. 31, 2016		(19,304)
Ending Balance at Dec. 31, 2016	1,481,598	$ (352,742)	45,376	254,512	1,534,983	(531)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends	(7,995)				(7,995)
Stock-Based Compensation (in shares)		3
Stock-Based Compensation	25,830	$ 48		25,782
Reissued Shares (in shares)		529
Reissued Shares	(2,720)	$ 7,531		(10,251)
Net Earnings	292,536				292,536
Foreign Currency Translation Adjustment	1,305					1,305
Repurchased Shares (in shares)		(1,961)
Repurchased Shares	(62,550)	$ (62,550)		0
Ending Balance (in shares) at Dec. 31, 2017		(20,733)
Ending Balance at Dec. 31, 2017	$ 1,728,004	$ (407,713)	$ 45,376	$ 270,043	$ 1,819,524	$ 774