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)