Revenue and Related Matters - Disaggregation of Revenue by Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Disaggregation of Revenue [Line Items]
Total revenues	$ 1,376,521	$ 1,167,319	$ 2,639,261	$ 2,271,357
Research
Disaggregation of Revenue [Line Items]
Total revenues	1,142,329	1,003,238	2,278,709	1,982,970
Conferences
Disaggregation of Revenue [Line Items]
Total revenues	113,525	58,179	123,879	82,981
Consulting
Disaggregation of Revenue [Line Items]
Total revenues	120,667	105,902	236,673	205,406
United States and Canada
Disaggregation of Revenue [Line Items]
Total revenues	912,753	746,365	1,729,723	1,454,783
United States and Canada | Research
Disaggregation of Revenue [Line Items]
Total revenues	752,670	646,432	1,493,199	1,277,765
United States and Canada | Conferences
Disaggregation of Revenue [Line Items]
Total revenues	87,267	40,328	94,919	59,927
United States and Canada | Consulting
Disaggregation of Revenue [Line Items]
Total revenues	72,816	59,605	141,605	117,091
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Total revenues	310,500	286,683	607,311	549,959
Europe, Middle East and Africa | Research
Disaggregation of Revenue [Line Items]
Total revenues	255,417	236,756	518,546	466,957
Europe, Middle East and Africa | Conferences
Disaggregation of Revenue [Line Items]
Total revenues	21,036	14,468	22,274	17,181
Europe, Middle East and Africa | Consulting
Disaggregation of Revenue [Line Items]
Total revenues	34,047	35,459	66,491	65,821
Other International
Disaggregation of Revenue [Line Items]
Total revenues	153,268	134,271	302,227	266,615
Other International | Research
Disaggregation of Revenue [Line Items]
Total revenues	134,242	120,050	266,964	238,248
Other International | Conferences
Disaggregation of Revenue [Line Items]
Total revenues	5,222	3,383	6,686	5,873
Other International | Consulting
Disaggregation of Revenue [Line Items]
Total revenues	$ 13,804	$ 10,838	$ 28,577	$ 22,494