Revenue and Related Matters - Timing Of Revenue Recognition Liabilities per Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Total revenues	$ 4,733,962	$ 4,099,403	$ 4,245,321
Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	4,075,639	3,609,657	3,399,978
Transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenues	658,323	489,746	845,343
Research
Disaggregation of Revenue [Line Items]
Total revenues	4,101,392	3,602,892	3,374,548
Research | Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	3,740,694	3,313,111	3,083,936
Research | Transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenues	360,698	289,781	290,612
Conferences
Disaggregation of Revenue [Line Items]
Total revenues	214,449	120,140	476,869
Conferences | Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Conferences | Transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenues	214,449	120,140	476,869
Consulting
Disaggregation of Revenue [Line Items]
Total revenues	418,121	376,371	393,904
Consulting | Transferred over time
Disaggregation of Revenue [Line Items]
Total revenues	334,945	296,546	316,042
Consulting | Transferred at a point in time
Disaggregation of Revenue [Line Items]
Total revenues	$ 83,176	$ 79,825	$ 77,862