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Recognized Amounts of Identifiable Assets Acquired and Liabilities Assumed (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Feb. 01, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Business Combination, Separately Recognized Transactions [Line Items]
Cash		$ 16,486
Accounts receivable and other tangible assets		12,934
Accounts payable and other liabilities		(9,653)
Deferred revenue	$ (2,349)	(2,349)		$ 0
Net deferred tax liabilities		(14,871)
Total identifiable net assets		80,577
Goodwill	$ 1,748,228	180,232	$ 1,572,455	$ 1,379,458	$ 1,378,553
Developed Software and Core Technologies
Business Combination, Separately Recognized Transactions [Line Items]
Finite-lived intangible assets		41,045
Customer Lists and Contract Backlog
Business Combination, Separately Recognized Transactions [Line Items]
Finite-lived intangible assets		31,516
Trade Names
Business Combination, Separately Recognized Transactions [Line Items]
Finite-lived intangible assets		5,469
Granta Design
Business Combination, Separately Recognized Transactions [Line Items]
Cash		13,644
Accounts receivable and other tangible assets		6,926
Accounts payable and other liabilities		(6,176)
Deferred revenue		(1,426)
Net deferred tax liabilities		(9,822)
Total identifiable net assets		60,186
Goodwill		138,537
Granta Design \| Developed Software and Core Technologies
Business Combination, Separately Recognized Transactions [Line Items]
Finite-lived intangible assets		32,445
Granta Design \| Customer Lists and Contract Backlog
Business Combination, Separately Recognized Transactions [Line Items]
Finite-lived intangible assets		20,016
Granta Design \| Trade Names
Business Combination, Separately Recognized Transactions [Line Items]
Finite-lived intangible assets		4,579
Helic
Business Combination, Separately Recognized Transactions [Line Items]
Cash		2,842
Accounts receivable and other tangible assets		6,008
Accounts payable and other liabilities		(3,477)
Deferred revenue		(923)
Net deferred tax liabilities		(5,049)
Total identifiable net assets		20,391
Goodwill		41,695
Helic \| Developed Software and Core Technologies
Business Combination, Separately Recognized Transactions [Line Items]
Finite-lived intangible assets		8,600
Helic \| Customer Lists and Contract Backlog
Business Combination, Separately Recognized Transactions [Line Items]
Finite-lived intangible assets		11,500
Helic \| Trade Names
Business Combination, Separately Recognized Transactions [Line Items]
Finite-lived intangible assets		$ 890