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, 2015		(18,152)
Beginning 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)
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)
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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends	(8,661)				(8,661)
Stock-Based Compensation	26,852			26,852
Reissued Shares (in shares)		915
Reissued Shares	(9,372)	$ 8,601		(17,973)
Net Earnings	196,210				196,210
Foreign Currency Translation Adjustment	(1,861)					(1,861)
Repurchased Shares (in shares)		(3,750)
Repurchased Shares	(168,735)	$ (168,735)
Ending Balance (in shares) at Dec. 31, 2018		(23,568)
Ending Balance at Dec. 31, 2018	1,760,708	$ (567,847)	$ 45,376	$ 278,922	2,005,344	$ (1,087)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Opening Balance Sheet Adjustment - ASC 606 | Accounting Standards Update 2014-09	$ (1,729)				$ (1,729)