Acquisitions - Recognized Amounts of Identifiable Assets Acquired and Liabilities Assumed 2019 (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019	Nov. 01, 2019	Feb. 01, 2019
Business Acquisition [Line Items]
Cash	$ 29,507,000	$ 28,395,000
Accounts receivable and other tangible assets	33,700,000	38,244,000
Accounts payable and other liabilities	(24,385,000)	(14,997,000)
Deferred revenue	(6,872,000)	(6,880,000)
Uncertain tax positions		(257,000)
Net deferred tax liabilities	(57,659,000)	(64,539,000)
Total identifiable net assets	236,977,000	284,018,000
Goodwill	593,055,000	844,770,000
Developed Software and Core Technologies
Business Acquisition [Line Items]
Finite-lived intangible assets	215,714,000	225,163,000
Customer Lists
Business Acquisition [Line Items]
Finite-lived intangible assets	27,016,000	61,659,000
Trade Names
Business Acquisition [Line Items]
Finite-lived intangible assets	$ 19,956,000	17,230,000
Livermore Software Technology Corporation
Business Acquisition [Line Items]
Cash			$ 8,520,000
Accounts receivable and other tangible assets			20,569,000
Accounts payable and other liabilities			(3,887,000)
Deferred revenue			(3,565,000)
Uncertain tax positions			0
Net deferred tax liabilities			(47,412,000)
Total identifiable net assets			178,425,000
Goodwill			603,079,000
Livermore Software Technology Corporation | Developed Software and Core Technologies
Business Acquisition [Line Items]
Finite-lived intangible assets			167,700,000
Livermore Software Technology Corporation | Customer Lists
Business Acquisition [Line Items]
Finite-lived intangible assets			25,900,000
Livermore Software Technology Corporation | Trade Names
Business Acquisition [Line Items]
Finite-lived intangible assets			$ 10,600,000
Granta Design
Business Acquisition [Line Items]
Cash				$ 13,644,000
Accounts receivable and other tangible assets				6,941,000
Accounts payable and other liabilities				(5,164,000)
Deferred revenue				(1,426,000)
Uncertain tax positions				0
Net deferred tax liabilities				(8,976,000)
Total identifiable net assets				62,059,000
Goodwill				146,677,000
Granta Design | Developed Software and Core Technologies
Business Acquisition [Line Items]
Finite-lived intangible assets				32,445,000
Granta Design | Customer Lists
Business Acquisition [Line Items]
Finite-lived intangible assets				20,016,000
Granta Design | Trade Names
Business Acquisition [Line Items]
Finite-lived intangible assets				$ 4,579,000
Other Acquisitions
Business Acquisition [Line Items]
Cash		6,231,000
Accounts receivable and other tangible assets		10,734,000
Accounts payable and other liabilities		(5,946,000)
Deferred revenue		(1,889,000)
Uncertain tax positions		(257,000)
Net deferred tax liabilities		(8,151,000)
Total identifiable net assets		43,534,000
Goodwill		95,014,000
Other Acquisitions | Developed Software and Core Technologies
Business Acquisition [Line Items]
Finite-lived intangible assets		25,018,000
Other Acquisitions | Customer Lists
Business Acquisition [Line Items]
Finite-lived intangible assets		15,743,000
Other Acquisitions | Trade Names
Business Acquisition [Line Items]
Finite-lived intangible assets		$ 2,051,000