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Segment Information - Information About Reportable Segments (Details) | 3 Months Ended
--- | ---
Mar. 31, 2024 USD ($) segment | Mar. 31, 2023 USD ($)
Segment Reporting Information [Line Items] |  |
Number of reportable segments | segment | 3 |
Operating income | $ 273,885,000 | $ 407,957,000
Intersegment Eliminations |  |
Segment Reporting Information [Line Items] |  |
Revenues | 0 |
Operating Segments |  |
Segment Reporting Information [Line Items] |  |
Revenues | 1,472,926,000 | 1,408,869,000
Operating income | 1,022,112,000 | 977,110,000
Operating Segments | Research |  |
Segment Reporting Information [Line Items] |  |
Revenues | 1,268,172,000 | 1,217,191,000
Operating income | 944,570,000 | 899,514,000
Operating Segments | Conferences |  |
Segment Reporting Information [Line Items] |  |
Revenues | 70,069,000 | 64,642,000
Operating income | 23,255,000 | 26,788,000
Operating Segments | Consulting |  |
Segment Reporting Information [Line Items] |  |
Revenues | 134,685,000 | 127,036,000
Operating income | 54,287,000 | 50,808,000
Corporate and Reconciling Items |  |
Segment Reporting Information [Line Items] |  |
Operating income | $ (748,227,000) | $ (569,153,000)

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