Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenues:
Total revenues	$ 4,733,962	$ 4,099,403	$ 4,245,321
Costs and expenses:
Cost of services and product development	1,444,093	1,345,024	1,550,568
Selling, general and administrative	2,155,658	2,038,963	2,103,424
Depreciation	102,802	93,925	82,066
Amortization of intangibles	109,603	125,059	129,713
Acquisition and integration charges	6,055	6,282	9,463
Total costs and expenses	3,818,211	3,609,253	3,875,234
Operating income	915,751	490,150	370,087
Interest income	1,893	2,087	3,026
Interest expense	(118,513)	(115,636)	(102,831)
Gain on event cancellation insurance claims	152,310	0	0
Loss from divested operations	0	0	(2,075)
Loss on extinguishment of debt	0	(44,814)	0
Other income (expense), net	18,429	(5,654)	7,532
Income before income taxes	969,870	326,133	275,739
Provision for income taxes	176,310	59,388	42,449
Net income	$ 793,560	$ 266,745	$ 233,290
Net income per share:
Basic (in dollars per share)	$ 9.33	$ 2.99	$ 2.60
Diluted (in dollars per share)	$ 9.21	$ 2.96	$ 2.56
Weighted average shares outstanding:
Basic (in shares)	85,026	89,315	89,817
Diluted (in shares)	86,177	90,017	90,971
Research
Revenues:
Total revenues	$ 4,101,392	$ 3,602,892	$ 3,374,548
Conferences
Revenues:
Total revenues	214,449	120,140	476,869
Consulting
Revenues:
Total revenues	$ 418,121	$ 376,371	$ 393,904