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Goodwill and Intangible Assets - Changes to the Carrying Amount of Goodwill by Segment (Details) - USD ($)
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Goodwill [Roll Forward]    
Beginning Balance $ 2,937,260,000 $ 2,930,211,000
Additions due to an acquisition   4,176,000
Foreign currency translation impact 7,055,000 2,873,000
Ending Balance 2,930,205,000 2,937,260,000
Accumulated goodwill impairment losses 0  
Research    
Goodwill [Roll Forward]    
Beginning Balance 2,657,549,000 2,651,193,000
Additions due to an acquisition   4,176,000
Foreign currency translation impact 6,568,000 2,180,000
Ending Balance 2,650,981,000 2,657,549,000
Conferences    
Goodwill [Roll Forward]    
Beginning Balance 183,997,000 183,951,000
Additions due to an acquisition   0
Foreign currency translation impact 77,000 46,000
Ending Balance 183,920,000 183,997,000
Consulting    
Goodwill [Roll Forward]    
Beginning Balance 95,714,000 95,067,000
Additions due to an acquisition   0
Foreign currency translation impact 410,000 647,000
Ending Balance $ 95,304,000 $ 95,714,000