Goodwill and Intangible Assets - Changes to the Carrying Amount of Goodwill by Segment (Details)	3 Months Ended	9 Months Ended
	Sep. 30, 2023 USD ($)	Sep. 30, 2023 USD ($)
Goodwill [Line Items]
Goodwill impairment	$ 0
Goodwill [Roll Forward]
Beginning balance		$ 2,930,211,000
Additions due to an acquisition		4,176,000
Foreign currency translation impact		(1,121,000)
Ending balance	2,933,266,000	2,933,266,000
Goodwill, accumulated impairment losses	0	0
Research
Goodwill [Roll Forward]
Beginning balance		2,651,193,000
Additions due to an acquisition		4,176,000
Foreign currency translation impact		(1,267,000)
Ending balance	2,654,102,000	2,654,102,000
Conferences
Goodwill [Roll Forward]
Beginning balance		183,951,000
Additions due to an acquisition		0
Foreign currency translation impact		0
Ending balance	183,951,000	183,951,000
Consulting
Goodwill [Roll Forward]
Beginning balance		95,067,000
Additions due to an acquisition		0
Foreign currency translation impact		146,000
Ending balance	$ 95,213,000	$ 95,213,000