Goodwill and Intangible Assets - Changes to the Carrying Amount of Goodwill by Segment (Details) - USD ($)	3 Months Ended
	Mar. 31, 2025	Dec. 31, 2024
Goodwill [Roll Forward]
Beginning balance	$ 2,930,205,000
Foreign currency translation impact	2,917,000
Ending balance	2,933,122,000
Goodwill, accumulated impairment losses	0	$ 0
Research
Goodwill [Roll Forward]
Beginning balance	2,650,981,000
Foreign currency translation impact	2,447,000
Ending balance	2,653,428,000
Conferences
Goodwill [Roll Forward]
Beginning balance	183,920,000
Foreign currency translation impact	38,000
Ending balance	183,958,000
Consulting
Goodwill [Roll Forward]
Beginning balance	95,304,000
Foreign currency translation impact	432,000
Ending balance	$ 95,736,000