Acquisitions - Recognized Amounts of Identifiable Assets Acquired and Liabilities Assumed 2020 (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 01, 2020	Apr. 01, 2020	Dec. 31, 2019
Cash	$ 29,507			$ 28,395
Accounts receivable and other tangible assets	33,700			38,244
Accounts payable and other liabilities	(24,385)			(14,997)
Deferred revenue	(6,872)			(6,880)
Net deferred tax liabilities	(57,659)			(64,539)
Total identifiable net assets	236,977			284,018
Goodwill	593,055			844,770
Developed Software and Core Technologies
Finite-lived intangible assets	215,714			225,163
Customer Lists
Finite-lived intangible assets	27,016			61,659
Trade Names
Finite-lived intangible assets	$ 19,956			$ 17,230
Analytical Graphics, Inc.
Cash		$ 17,663
Accounts receivable and other tangible assets		29,456
Accounts payable and other liabilities		(23,279)
Deferred revenue		(5,467)
Net deferred tax liabilities		(50,207)
Total identifiable net assets		195,866
Goodwill		526,621
Analytical Graphics, Inc. | Developed Software and Core Technologies
Finite-lived intangible assets		184,100
Analytical Graphics, Inc. | Customer Lists
Finite-lived intangible assets		25,400
Analytical Graphics, Inc. | Trade Names
Finite-lived intangible assets		$ 18,200
Lumerical
Cash			$ 11,844
Accounts receivable and other tangible assets			4,244
Accounts payable and other liabilities			(1,106)
Deferred revenue			(1,405)
Net deferred tax liabilities			(7,452)
Total identifiable net assets			41,111
Goodwill			66,434
Lumerical | Developed Software and Core Technologies
Finite-lived intangible assets			31,614
Lumerical | Customer Lists
Finite-lived intangible assets			1,616
Lumerical | Trade Names
Finite-lived intangible assets			$ 1,756