Revenue and Related Matters - Disaggregation of Revenue by Geographic Area (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Disaggregation of Revenue [Line Items]
Total revenues	$ 6,497,226	$ 6,267,411	$ 5,906,956
United States and Canada
Disaggregation of Revenue [Line Items]
Total revenues	4,032,601	4,017,730	3,911,042
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenues	1,693,732	1,517,815	1,332,070
Other International
Disaggregation of Revenue [Line Items]
Total revenues	770,893	731,866	663,844
Insights
Disaggregation of Revenue [Line Items]
Total revenues	5,072,570	4,829,051	4,516,035
Insights | United States and Canada
Disaggregation of Revenue [Line Items]
Total revenues	3,117,883	3,077,133	2,973,062
Insights | Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenues	1,323,266	1,169,314	1,009,500
Insights | Other International
Disaggregation of Revenue [Line Items]
Total revenues	631,421	582,604	533,473
Conferences
Disaggregation of Revenue [Line Items]
Total revenues	644,743	583,224	505,164
Conferences | United States and Canada
Disaggregation of Revenue [Line Items]
Total revenues	381,544	354,011	317,531
Conferences | Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenues	194,995	165,306	140,640
Conferences | Other International
Disaggregation of Revenue [Line Items]
Total revenues	68,204	63,907	46,993
Consulting
Disaggregation of Revenue [Line Items]
Total revenues	552,499	558,537	514,746
Consulting | United States and Canada
Disaggregation of Revenue [Line Items]
Total revenues	342,287	343,840	317,645
Consulting | Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenues	148,946	142,849	130,471
Consulting | Other International
Disaggregation of Revenue [Line Items]
Total revenues	61,266	71,848	66,630
Other
Disaggregation of Revenue [Line Items]
Total revenues	227,414	296,599	371,011
Other | United States and Canada
Disaggregation of Revenue [Line Items]
Total revenues	190,887	242,746	302,804
Other | Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenues	26,525	40,346	51,459
Other | Other International
Disaggregation of Revenue [Line Items]
Total revenues	$ 10,002	$ 13,507	$ 16,748