Revenue and Related Matters - Timing Of Revenue Recognition Liabilities per Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Disaggregation of Revenue [Line Items]
Total revenues	$ 1,408,784	$ 1,331,868	$ 4,320,838	$ 3,971,129
Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	1,225,004	1,135,741	3,649,056	3,391,052
Transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenues	183,780	196,127	671,782	580,077
Research
Disaggregation of Revenue [Line Items]
Total revenues	1,218,739	1,147,823	3,643,815	3,426,532
Research | Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	1,125,285	1,045,425	3,348,409	3,109,099
Research | Transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenues	93,454	102,398	295,406	317,433
Conferences
Disaggregation of Revenue [Line Items]
Total revenues	57,200	77,031	290,739	200,910
Conferences | Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Conferences | Transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenues	57,200	77,031	290,739	200,910
Consulting
Disaggregation of Revenue [Line Items]
Total revenues	132,845	107,014	386,284	343,687
Consulting | Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	99,719	90,316	300,647	281,953
Consulting | Transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenues	$ 33,126	$ 16,698	$ 85,637	$ 61,734