Revenue and Related Matters - Disaggregation of Revenue by Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Disaggregation of Revenue [Line Items]
Total revenues	$ 1,484,306	$ 1,408,784	$ 4,552,292	$ 4,320,838
United States and Canada
Disaggregation of Revenue [Line Items]
Total revenues	923,834	917,462	2,940,465	2,864,991
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenues	369,039	321,713	1,072,472	963,438
Other International
Disaggregation of Revenue [Line Items]
Total revenues	191,433	169,609	539,355	492,409
Research
Disaggregation of Revenue [Line Items]
Total revenues	1,280,908	1,218,739	3,815,072	3,643,815
Research | United States and Canada
Disaggregation of Revenue [Line Items]
Total revenues	836,195	822,401	2,504,135	2,444,524
Research | Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenues	297,916	261,813	873,109	788,725
Research | Other International
Disaggregation of Revenue [Line Items]
Total revenues	146,797	134,525	437,828	410,566
Conferences
Disaggregation of Revenue [Line Items]
Total revenues	75,776	57,200	331,929	290,739
Conferences | United States and Canada
Disaggregation of Revenue [Line Items]
Total revenues	8,191	7,652	187,400	179,670
Conferences | Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenues	40,486	30,398	97,443	78,408
Conferences | Other International
Disaggregation of Revenue [Line Items]
Total revenues	27,099	19,150	47,086	32,661
Consulting
Disaggregation of Revenue [Line Items]
Total revenues	127,622	132,845	405,291	386,284
Consulting | United States and Canada
Disaggregation of Revenue [Line Items]
Total revenues	79,448	87,409	248,930	240,797
Consulting | Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenues	30,637	29,502	101,920	96,305
Consulting | Other International
Disaggregation of Revenue [Line Items]
Total revenues	$ 17,537	$ 15,934	$ 54,441	$ 49,182