Goodwill and Intangible Assets - Changes to the Carrying Amount of Goodwill by Segment (Details) - USD ($)	9 Months Ended
	Sep. 30, 2024	Dec. 31, 2023
Goodwill [Roll Forward]
Beginning balance	$ 2,937,260,000
Foreign currency translation impact	520,000
Ending balance	2,937,780,000
Goodwill, accumulated impairment losses	0	$ 0
Research
Goodwill [Roll Forward]
Beginning balance	2,657,549,000
Foreign currency translation impact	78,000
Ending balance	2,657,627,000
Conferences
Goodwill [Roll Forward]
Beginning balance	183,997,000
Foreign currency translation impact	1,000
Ending balance	183,998,000
Consulting
Goodwill [Roll Forward]
Beginning balance	95,714,000
Foreign currency translation impact	441,000
Ending balance	$ 96,155,000