Revenue and Related Matters - Timing Of Revenue Recognition Liabilities per Segment (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
Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	1,133,065	1,002,743	2,255,311	1,981,172
Transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenues	243,456	164,576	383,950	290,185
Research
Disaggregation of Revenue [Line Items]
Total revenues	1,142,329	1,003,238	2,278,709	1,982,970
Research | Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	1,037,864	916,754	2,063,674	1,810,841
Research | Transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenues	104,465	86,484	215,035	172,129
Conferences
Disaggregation of Revenue [Line Items]
Total revenues	113,525	58,179	123,879	82,981
Conferences | Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0	0
Conferences | Transferred at a point in time
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
Consulting | Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	95,201	85,989	191,637	170,331
Consulting | Transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenues	$ 25,466	$ 19,913	$ 45,036	$ 35,075