Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenues:
Total revenues	$ 1,156,282	$ 994,618	$ 3,427,639	$ 2,986,644
Costs and expenses:
Cost of services and product development	359,237	329,767	1,044,506	993,596
Selling, general and administrative	512,573	521,508	1,488,324	1,512,987
Depreciation	25,371	22,743	76,972	67,988
Amortization of intangibles	27,109	31,228	83,777	94,615
Acquisition and integration charges	1,771	1,722	3,713	5,438
Total costs and expenses	926,061	906,968	2,697,292	2,674,624
Operating income	230,221	87,650	730,347	312,020
Interest expense, net	(31,599)	(30,538)	(85,138)	(87,182)
Gain on event cancellation insurance claims	0	0	135,545	0
Loss on extinguishment of debt	0	(44,814)	0	(44,814)
Other income (expense), net	211	1,869	12,019	(10,046)
Income before income taxes	198,833	14,167	792,773	169,978
Provision (benefit) for income taxes	49,968	(2,797)	208,572	22,840
Net income	$ 148,865	$ 16,964	$ 584,201	$ 147,138
Net income per share:
Basic (in dollars per share)	$ 1.78	$ 0.19	$ 6.80	$ 1.65
Diluted (in dollars per share)	$ 1.76	$ 0.19	$ 6.72	$ 1.63
Weighted average shares outstanding:
Basic (in shares)	83,566	89,378	85,877	89,307
Diluted (in shares)	84,766	89,955	86,925	90,002
Research
Revenues:
Total revenues	$ 1,037,124	$ 892,719	$ 3,020,094	$ 2,677,339
Conferences
Revenues:
Total revenues	24,415	12,738	107,396	26,925
Consulting
Revenues:
Total revenues	$ 94,743	$ 89,161	$ 300,149	$ 282,380