Segment Information - Information About Reportable Segments (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2022 USD ($) segment	Sep. 30, 2021 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segment			3
Operating income	$ 253,418,000	$ 230,221,000	$ 767,787,000	$ 730,347,000
Intersegment revenues
Segment Reporting Information [Line Items]
Revenues			0
Reportable segments
Segment Reporting Information [Line Items]
Revenues	1,331,868,000	1,156,282,000	3,971,129,000	3,427,639,000
Operating income	925,969,000	811,519,000	2,791,198,000	2,416,388,000
Corporate and other expenses
Segment Reporting Information [Line Items]
Operating income	(672,551,000)	(581,298,000)	(2,023,411,000)	(1,686,041,000)
Research | Reportable segments
Segment Reporting Information [Line Items]
Revenues	1,147,823,000	1,037,124,000	3,426,532,000	3,020,094,000
Operating income	848,438,000	769,091,000	2,541,782,000	2,235,594,000
Conferences | Reportable segments
Segment Reporting Information [Line Items]
Revenues	77,031,000	24,415,000	200,910,000	107,396,000
Operating income	40,318,000	11,456,000	110,968,000	67,954,000
Consulting | Reportable segments
Segment Reporting Information [Line Items]
Revenues	107,014,000	94,743,000	343,687,000	300,149,000
Operating income	$ 37,213,000	$ 30,972,000	$ 138,448,000	$ 112,840,000