Revenue and Related Matters - Disaggregation of Revenue by Geographic Area (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disaggregation of Revenue [Line Items]
Total revenues	$ 5,906,956	$ 5,475,846	$ 4,733,962
United States and Canada
Disaggregation of Revenue [Line Items]
Total revenues	3,911,042	3,619,382	3,048,902
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenues	1,332,070	1,234,659	1,130,979
Other International
Disaggregation of Revenue [Line Items]
Total revenues	663,844	621,805	554,081
Research
Disaggregation of Revenue [Line Items]
Total revenues	4,887,046	4,604,791	4,101,392
Research | United States and Canada
Disaggregation of Revenue [Line Items]
Total revenues	3,275,866	3,056,096	2,655,534
Research | Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenues	1,060,959	1,017,860	958,339
Research | Other International
Disaggregation of Revenue [Line Items]
Total revenues	550,221	530,835	487,519
Conferences
Disaggregation of Revenue [Line Items]
Total revenues	505,164	389,273	214,449
Conferences | United States and Canada
Disaggregation of Revenue [Line Items]
Total revenues	317,531	263,165	146,707
Conferences | Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenues	140,640	88,979	47,883
Conferences | Other International
Disaggregation of Revenue [Line Items]
Total revenues	46,993	37,129	19,859
Consulting
Disaggregation of Revenue [Line Items]
Total revenues	514,746	481,782	418,121
Consulting | United States and Canada
Disaggregation of Revenue [Line Items]
Total revenues	317,645	300,121	246,661
Consulting | Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenues	130,471	127,820	124,757
Consulting | Other International
Disaggregation of Revenue [Line Items]
Total revenues	$ 66,630	$ 53,841	$ 46,703