Goodwill and Intangible Assets - Changes to the Carrying Amount of Goodwill by Segment (Details) - USD ($)	6 Months Ended
	Jun. 30, 2024	Dec. 31, 2023
Goodwill [Roll Forward]
Beginning balance	$ 2,937,260,000
Foreign currency translation impact	(3,038,000)
Ending balance	2,934,222,000
Goodwill, accumulated impairment losses	0	$ 0
Research
Goodwill [Roll Forward]
Beginning balance	2,657,549,000
Foreign currency translation impact	(2,789,000)
Ending balance	2,654,760,000
Conferences
Goodwill [Roll Forward]
Beginning balance	183,997,000
Foreign currency translation impact	(43,000)
Ending balance	183,954,000
Consulting
Goodwill [Roll Forward]
Beginning balance	95,714,000
Foreign currency translation impact	(206,000)
Ending balance	$ 95,508,000