CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive (Loss)/Income
Beginning balance at Dec. 31, 2016	$ 2,208,405	$ 932	$ 883,010	$ 2,057,665	$ (675,550)	$ (57,652)
Beginning balance, shares at Dec. 31, 2016		93,236			7,548
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury shares acquired	$ (336,042)				$ (336,042)
Treasury shares acquired, shares	2,750				2,750
Stock-based compensation, activity			(9,653)
Stock-based compensation activity	$ 94,409				$ 104,062
Stock-based compensation activity, shares					(1,254)
Other comprehensive (loss)/income	19,808					19,808
Net income for the year	259,251			259,251
Ending balance at Dec. 31, 2017	2,245,831	$ 932	873,357	2,316,916	$ (907,530)	(37,844)
Ending balance, shares at Dec. 31, 2017		93,236			9,044
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury shares acquired	$ (269,801)				$ (269,801)
Treasury shares acquired, shares	1,674				1,674
Stock-based compensation, activity			(5,895)
Stock-based compensation activity	$ 95,557				$ 101,452
Stock-based compensation activity, shares					(1,116)
Other comprehensive (loss)/income	(24,535)					(24,535)
Net income for the year	419,375			419,375
Ending balance at Dec. 31, 2018	2,649,547	$ 932	867,462	2,919,411	$ (1,075,879)	(62,379)
Ending balance, shares at Dec. 31, 2018		93,236			9,602
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Acquisition of Livermore Software Technology, LLC	307,173	$ 14	307,159
Acquisition of Livermore Software Technology, LLC, shares		1,392
Treasury shares acquired	$ (59,116)				$ (59,116)
Treasury shares acquired, shares	330				330
Stock-based compensation, activity			14,318
Stock-based compensation activity	$ 107,482				$ 93,164
Stock-based compensation activity, shares					(1,039)
Other comprehensive (loss)/income	(3,002)					(3,002)
Net income for the year	451,295			451,295
Ending balance at Dec. 31, 2019	$ 3,453,379	$ 946	$ 1,188,939	$ 3,370,706	$ (1,041,831)	$ (65,381)
Ending balance, shares at Dec. 31, 2019		94,628			8,893