Revenue and Related Matters - Timing Of Revenue Recognition Liabilities per Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Total revenues	$ 1,262,740	$ 1,104,038
Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	1,122,246	978,429
Transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenues	140,494	125,609
Research
Disaggregation of Revenue [Line Items]
Total revenues	1,136,380	979,732
Research | Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	1,025,810	894,087
Research | Transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenues	110,570	85,645
Conferences
Disaggregation of Revenue [Line Items]
Total revenues	10,354	24,802
Conferences | Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	0	0
Conferences | Transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenues	10,354	24,802
Consulting
Disaggregation of Revenue [Line Items]
Total revenues	116,006	99,504
Consulting | Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	96,436	84,342
Consulting | Transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenues	$ 19,570	$ 15,162