CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Livermore Software Technology Corporation	Analytical Graphics, Inc.	Common Stock	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	Treasury Stock	Treasury Stock Livermore Software Technology Corporation	Accumulated Other Comprehensive (Loss)/Income
Beginning balance at Dec. 31, 2019	$ 3,453,379			$ 946		$ 1,188,939			$ 3,370,706	$ (1,041,831)		$ (65,381)
Beginning balance, shares at Dec. 31, 2019				94,628						8,893
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury shares acquired	(161,029)									$ (161,029)
Treasury shares acquired, shares										690
Stock-based compensation activity	(21,772)					(70,769)				$ 48,997
Stock-based compensation activity, shares										(541)
Other comprehensive (loss)/income	(24,292)											(24,292)
Net income	46,064								46,064
Ending balance at Mar. 31, 2020	3,292,350			$ 946		1,118,170			3,416,770	$ (1,153,863)		(89,673)
Ending balance, shares at Mar. 31, 2020				94,628						9,042
Beginning balance at Dec. 31, 2019	3,453,379			$ 946		1,188,939			3,370,706	$ (1,041,831)		(65,381)
Beginning balance, shares at Dec. 31, 2019				94,628						8,893
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury shares acquired	$ (161,029)
Treasury shares acquired, shares	690
Net income	$ 142,628
Ending balance at Jun. 30, 2020	3,438,048			$ 946		1,144,193			3,513,334	$ (1,141,040)		(79,385)
Ending balance, shares at Jun. 30, 2020				94,628						8,890
Beginning balance at Mar. 31, 2020	3,292,350			$ 946		1,118,170			3,416,770	$ (1,153,863)		(89,673)
Beginning balance, shares at Mar. 31, 2020				94,628						9,042
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Acquisition activity		$ 1,531					$ 1,030				$ 501
Acquisition activity, treasury shares											(6)
Stock-based compensation activity	37,315					24,993				$ 12,322
Stock-based compensation activity, shares										(146)
Other comprehensive (loss)/income	10,288											10,288
Net income	96,564								96,564
Ending balance at Jun. 30, 2020	3,438,048			$ 946		1,144,193			3,513,334	$ (1,141,040)		(79,385)
Ending balance, shares at Jun. 30, 2020				94,628						8,890
Beginning balance at Dec. 31, 2020	4,097,872			$ 953		1,434,203			3,804,593	$ (1,124,102)		(17,775)
Beginning balance, shares at Dec. 31, 2020				95,266						8,694
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation activity	(39,037)					(87,602)				$ 48,565
Stock-based compensation activity, shares										(565)
Other comprehensive (loss)/income	(19,264)											(19,264)
Net income	72,398								72,398
Ending balance at Mar. 31, 2021	4,111,969			$ 953		1,346,601			3,876,991	$ (1,075,537)		(37,039)
Ending balance, shares at Mar. 31, 2021				95,266						8,129
Beginning balance at Dec. 31, 2020	4,097,872			$ 953		1,434,203			3,804,593	$ (1,124,102)		(17,775)
Beginning balance, shares at Dec. 31, 2020				95,266						8,694
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury shares acquired	$ 0
Treasury shares acquired, shares	0
Net income	$ 166,114
Ending balance at Jun. 30, 2021	4,250,218			$ 953		1,381,590			3,970,707	$ (1,070,210)		(32,822)
Ending balance, shares at Jun. 30, 2021				95,267						8,066
Beginning balance at Mar. 31, 2021	4,111,969			$ 953		1,346,601			3,876,991	$ (1,075,537)		(37,039)
Beginning balance, shares at Mar. 31, 2021				95,266						8,129
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Acquisition activity			$ 328					$ 328
Acquisition activity, common shares					1
Stock-based compensation activity	39,988					34,661				$ 5,327
Stock-based compensation activity, shares										(63)
Other comprehensive (loss)/income	4,217											4,217
Net income	93,716								93,716
Ending balance at Jun. 30, 2021	$ 4,250,218			$ 953		$ 1,381,590			$ 3,970,707	$ (1,070,210)		$ (32,822)
Ending balance, shares at Jun. 30, 2021				95,267						8,066