CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Livermore Software Technology Corporation	Analytical Graphics, Inc.	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Common Stock Livermore Software Technology Corporation	Common Stock Analytical Graphics, Inc.	Additional Paid-In Capital	Additional Paid-In Capital Livermore Software Technology Corporation	Additional Paid-In Capital Analytical Graphics, Inc.	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Treasury Stock	Treasury Stock Livermore Software Technology Corporation	Treasury Stock Analytical Graphics, Inc.	Accumulated Other Comprehensive (Loss)/Income
Beginning balance at Dec. 31, 2017	$ 2,245,831			$ 183,120	$ 932			$ 873,357			$ 2,316,916	$ 183,120	$ (907,530)			$ (37,844)
Beginning 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 activity		$ 307,173				$ 14			$ 307,159
Acquisition activity, common 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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Acquisition activity		$ 1,531	$ 218,348				$ 7		$ 1,030	$ 218,108				$ 501	$ 233
Acquisition activity, common shares							638
Acquisition activity, treasury shares														(6)	(3)
Treasury shares acquired	$ (161,029)												$ (161,029)
Treasury shares acquired, shares	690												690
Stock-based compensation, activity								26,126
Stock-based compensation activity	$ 104,150												$ 78,024
Stock-based compensation activity, shares													(880)
Other comprehensive (loss)/income	47,606															47,606
Net income for the year	433,887										433,887
Ending balance at Dec. 31, 2020	$ 4,097,872				$ 953			$ 1,434,203			$ 3,804,593		$ (1,124,102)			$ (17,775)
Ending balance, shares at Dec. 31, 2020					95,266								8,694