Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Revenues:
Total revenues	$ 1,167,319	$ 973,135	$ 2,271,357	$ 1,992,026
Costs and expenses:
Cost of services and product development	350,802	322,551	685,269	663,829
Selling, general and administrative	488,496	494,840	975,751	991,479
Depreciation	25,851	22,728	51,601	45,245
Amortization of intangibles	26,154	31,208	56,668	63,387
Acquisition and integration charges	1,302	2,157	1,942	3,716
Total costs and expenses	892,605	873,484	1,771,231	1,767,656
Operating income	274,714	99,651	500,126	224,370
Interest expense, net	(27,390)	(30,296)	(53,539)	(56,644)
Gain on event cancellation insurance claims	135,545	0	135,545	0
Other (expense) income, net	(3,682)	(10,399)	11,808	(11,915)
Income before income taxes	379,187	58,956	593,940	155,811
Provision for income taxes	107,951	3,879	158,604	25,637
Net income	$ 271,236	$ 55,077	$ 435,336	$ 130,174
Net income per share:
Basic (in dollars per share)	$ 3.16	$ 0.62	$ 5.00	$ 1.46
Diluted (in dollars per share)	$ 3.13	$ 0.61	$ 4.95	$ 1.45
Weighted average shares outstanding:
Basic (in shares)	85,712	89,323	87,032	89,271
Diluted (in shares)	86,589	89,780	87,921	89,967
Research
Revenues:
Total revenues	$ 1,003,238	$ 875,329	$ 1,982,970	$ 1,784,620
Conferences
Revenues:
Total revenues	58,179	317	82,981	14,187
Consulting
Revenues:
Total revenues	$ 105,902	$ 97,489	$ 205,406	$ 193,219