Goodwill and Intangible Assets - Changes to Carrying Amount of Goodwill by Reporting Unit (Details) - USD ($)	3 Months Ended	6 Months Ended
	Sep. 30, 2021	Jun. 30, 2022
Goodwill [Line Items]
Goodwill impairment	$ 0
Goodwill [Roll Forward]
Beginning balance		$ 2,951,317,000
Foreign currency translation impact		(8,060,000)
Ending balance		2,943,257,000
Goodwill, accumulated impairment losses		0
Research
Goodwill [Roll Forward]
Beginning balance		2,670,934,000
Foreign currency translation impact		(6,795,000)
Ending balance		2,664,139,000
Conferences
Goodwill [Roll Forward]
Beginning balance		184,021,000
Foreign currency translation impact		(79,000)
Ending balance		183,942,000
Consulting
Goodwill [Roll Forward]
Beginning balance		96,362,000
Foreign currency translation impact		(1,186,000)
Ending balance		$ 95,176,000