Goodwill and Intangible Assets - Changes to the Carrying Amount of Goodwill by Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Goodwill [Roll Forward]
Beginning Balance	$ 2,951,317	$ 2,945,547
Additions due to acquisition	4,617	11,486
Foreign currency translation impact	(9,723)	(5,716)
Reclassified as held-for-sale	(16,000)
Ending Balance	2,930,211	2,951,317
Research
Goodwill [Roll Forward]
Beginning Balance	2,670,934	2,664,732
Additions due to acquisition	4,617	11,486
Foreign currency translation impact	(8,358)	(5,284)
Reclassified as held-for-sale	(16,000)
Ending Balance	2,651,193	2,670,934
Conferences
Goodwill [Roll Forward]
Beginning Balance	184,021	184,091
Additions due to acquisition	0	0
Foreign currency translation impact	(70)	(70)
Reclassified as held-for-sale	0
Ending Balance	183,951	184,021
Consulting
Goodwill [Roll Forward]
Beginning Balance	96,362	96,724
Additions due to acquisition	0	0
Foreign currency translation impact	(1,295)	(362)
Reclassified as held-for-sale	0
Ending Balance	$ 95,067	$ 96,362