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Acquisitions - Additional Information (Detail) - SiriusDecisions, Inc [Member] $ in Millions |  | 9 Months Ended
--- | --- | ---
Jan. 03, 2019 USD ($) Employee | Sep. 30, 2019 USD ($)
Business Acquisition [Line Items] |  |
Percentage of issued and outstanding shares acquired | 100.00% |
Number of employees | Employee | 350 |
Purchase price paid | $ 246.8 |
Acquisition costs recognized |  | $ 1.7

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