Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Acquisitions - Summary of Preliminary Allocation of Purchase Price to Fair Value of Assets Acquired and Liabilities Assumed (Parenthetical) (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
	Jan. 03, 2019	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Business Acquisition [Line Items]
Amortization of intangible assets		$ 5,099	$ 182	$ 11,309	$ 368
SiriusDecisions, Inc [Member]
Business Acquisition [Line Items]
Acquired intangible assets	$ 115,000
Acquired intangible assets, Useful life	8 years 4 months 24 days
Amortization of intangible assets		$ 4,900		$ 10,900
SiriusDecisions, Inc [Member] \| Technology Asset Class [Member]
Business Acquisition [Line Items]
Acquired intangible assets	$ 13,000
Acquired intangible assets, Useful life	3 years 2 months 12 days
SiriusDecisions, Inc [Member] \| Technology Asset Class [Member] \| Minimum [Member]
Business Acquisition [Line Items]
Acquired intangible assets, Useful life	1 year
SiriusDecisions, Inc [Member] \| Technology Asset Class [Member] \| Maximum [Member]
Business Acquisition [Line Items]
Acquired intangible assets, Useful life	8 years
SiriusDecisions, Inc [Member] \| Customer Relationships [Member]
Business Acquisition [Line Items]
Acquired intangible assets	$ 77,000
Acquired intangible assets, Useful life	9 years 3 months
SiriusDecisions, Inc [Member] \| Trade Names [Member]
Business Acquisition [Line Items]
Acquired intangible assets	$ 12,000
Acquired intangible assets, Useful life	15 years 6 months
SiriusDecisions, Inc [Member] \| Backlog [Member]
Business Acquisition [Line Items]
Acquired intangible assets	$ 13,000
Acquired intangible assets, Useful life	2 years