Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Revenues:
Total revenues	$ 5,906,956	$ 5,475,846	$ 4,733,962
Costs and expenses:
Cost of services and product development	1,903,240	1,693,771	1,444,093
Selling, general and administrative	2,701,542	2,480,944	2,155,658
Depreciation	98,645	93,410	102,802
Amortization of intangibles	92,458	98,536	109,603
Acquisition and integration charges	9,587	9,079	6,055
Gain from sale of divested operation	(135,410)	0	0
Total costs and expenses	4,670,062	4,375,740	3,818,211
Operating income	1,236,894	1,100,106	915,751
Interest income	38,526	4,880	1,893
Interest expense	(132,772)	(126,203)	(118,513)
Gain on event cancellation insurance claims	3,077	0	152,310
Other income, net	1,404	48,412	18,429
Income before income taxes	1,147,129	1,027,195	969,870
Provision for income taxes	264,663	219,396	176,310
Net income	$ 882,466	$ 807,799	$ 793,560
Net income per share:
Basic (in dollars per share)	$ 11.17	$ 10.08	$ 9.33
Diluted (in dollars per share)	$ 11.08	$ 9.96	$ 9.21
Weighted average shares outstanding:
Basic (in shares)	79,004	80,178	85,026
Diluted (in shares)	79,680	81,067	86,177
Research
Revenues:
Total revenues	$ 4,887,046	$ 4,604,791	$ 4,101,392
Conferences
Revenues:
Total revenues	505,164	389,273	214,449
Consulting
Revenues:
Total revenues	$ 514,746	$ 481,782	$ 418,121