Revenue and Related Matters - Timing Of Revenue Recognition Liabilities per Segment (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
Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	1,217,249	1,133,065	2,424,052	2,255,311
Transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenues	285,936	243,456	488,002	383,950
Research
Disaggregation of Revenue [Line Items]
Total revenues	1,207,885	1,142,329	2,425,076	2,278,709
Research | Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	1,113,328	1,037,864	2,223,124	2,063,674
Research | Transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenues	94,557	104,465	201,952	215,035
Conferences
Disaggregation of Revenue [Line Items]
Total revenues	168,897	113,525	233,539	123,879
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	168,897	113,525	233,539	123,879
Consulting
Disaggregation of Revenue [Line Items]
Total revenues	126,403	120,667	253,439	236,673
Consulting | Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	103,921	95,201	200,928	191,637
Consulting | Transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenues	$ 22,482	$ 25,466	$ 52,511	$ 45,036