Goodwill and Intangible Assets - Changes to the Carrying Amount of Goodwill by Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Goodwill [Roll Forward]
Beginning Balance	$ 2,945,547	$ 2,937,726
Additions due to acquisition	11,486
Foreign currency translation impact and other	(5,716)	7,821
Ending Balance	2,951,317	2,945,547
Research
Goodwill [Roll Forward]
Beginning Balance	2,664,732	2,651,060
Additions due to acquisition	11,486
Foreign currency translation impact and other	(5,284)	13,672
Ending Balance	2,670,934	2,664,732
Conferences
Goodwill [Roll Forward]
Beginning Balance	184,091	189,641
Additions due to acquisition	0
Foreign currency translation impact and other	(70)	(5,550)
Ending Balance	184,021	184,091
Consulting
Goodwill [Roll Forward]
Beginning Balance	96,724	97,025
Additions due to acquisition	0
Foreign currency translation impact and other	(362)	(301)
Ending Balance	$ 96,362	$ 96,724