Revenue and Related Matters - Disaggregation of Revenue by Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Disaggregation of Revenue [Line Items]
Total revenues	$ 1,503,185	$ 1,376,521	$ 2,912,054	$ 2,639,261
United States and Canada
Disaggregation of Revenue [Line Items]
Total revenues	1,012,380	912,753	1,947,529	1,729,723
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenues	330,923	310,500	641,725	607,311
Other International
Disaggregation of Revenue [Line Items]
Total revenues	159,882	153,268	322,800	302,227
Research
Disaggregation of Revenue [Line Items]
Total revenues	1,207,885	1,142,329	2,425,076	2,278,709
Research | United States and Canada
Disaggregation of Revenue [Line Items]
Total revenues	812,724	752,670	1,622,123	1,493,199
Research | Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenues	258,255	255,417	526,912	518,546
Research | Other International
Disaggregation of Revenue [Line Items]
Total revenues	136,906	134,242	276,041	266,964
Conferences
Disaggregation of Revenue [Line Items]
Total revenues	168,897	113,525	233,539	123,879
Conferences | United States and Canada
Disaggregation of Revenue [Line Items]
Total revenues	123,243	87,267	172,018	94,919
Conferences | Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenues	38,803	21,036	48,010	22,274
Conferences | Other International
Disaggregation of Revenue [Line Items]
Total revenues	6,851	5,222	13,511	6,686
Consulting
Disaggregation of Revenue [Line Items]
Total revenues	126,403	120,667	253,439	236,673
Consulting | United States and Canada
Disaggregation of Revenue [Line Items]
Total revenues	76,413	72,816	153,388	141,605
Consulting | Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenues	33,865	34,047	66,803	66,491
Consulting | Other International
Disaggregation of Revenue [Line Items]
Total revenues	$ 16,125	$ 13,804	$ 33,248	$ 28,577