Revenue and Related Matters - Disaggregation of Revenue by Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Disaggregation of Revenue [Line Items]
Total revenues	$ 1,331,868	$ 1,156,282	$ 3,971,129	$ 3,427,639
Research
Disaggregation of Revenue [Line Items]
Total revenues	1,147,823	1,037,124	3,426,532	3,020,094
Conferences
Disaggregation of Revenue [Line Items]
Total revenues	77,031	24,415	200,910	107,396
Consulting
Disaggregation of Revenue [Line Items]
Total revenues	107,014	94,743	343,687	300,149
United States and Canada
Disaggregation of Revenue [Line Items]
Total revenues	883,227	742,403	2,612,950	2,197,186
United States and Canada | Research
Disaggregation of Revenue [Line Items]
Total revenues	771,534	671,517	2,264,733	1,949,282
United States and Canada | Conferences
Disaggregation of Revenue [Line Items]
Total revenues	44,499	14,171	139,418	74,098
United States and Canada | Consulting
Disaggregation of Revenue [Line Items]
Total revenues	67,194	56,715	208,799	173,806
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenues	289,771	276,955	897,082	826,914
Europe, Middle East and Africa | Research
Disaggregation of Revenue [Line Items]
Total revenues	245,093	242,273	763,639	709,230
Europe, Middle East and Africa | Conferences
Disaggregation of Revenue [Line Items]
Total revenues	18,034	7,975	40,308	25,156
Europe, Middle East and Africa | Consulting
Disaggregation of Revenue [Line Items]
Total revenues	26,644	26,707	93,135	92,528
Other International
Disaggregation of Revenue [Line Items]
Total revenues	158,870	136,924	461,097	403,539
Other International | Research
Disaggregation of Revenue [Line Items]
Total revenues	131,196	123,334	398,160	361,582
Other International | Conferences
Disaggregation of Revenue [Line Items]
Total revenues	14,498	2,269	21,184	8,142
Other International | Consulting
Disaggregation of Revenue [Line Items]
Total revenues	$ 13,176	$ 11,321	$ 41,753	$ 33,815