Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues:
Total revenues	$ 4,099,403	$ 4,245,321	$ 3,975,454
Costs and expenses:
Cost of services and product development	1,345,024	1,550,568	1,468,800
Selling, general and administrative	2,038,963	2,103,424	1,884,141
Depreciation	93,925	82,066	68,592
Amortization of intangibles	125,059	129,713	187,009
Acquisition and integration charges	6,282	9,463	107,197
Total costs and expenses	3,609,253	3,875,234	3,715,739
Operating income	490,150	370,087	259,715
Interest income	2,087	3,026	2,566
Interest expense	(115,636)	(102,831)	(126,774)
(Loss) gain from divested operations	0	(2,075)	45,447
Loss on extinguishment of debt	(44,814)	0	0
Other (expense) income, net	(5,654)	7,532	167
Income before income taxes	326,133	275,739	181,121
Provision for income taxes	59,388	42,449	58,665
Net income	$ 266,745	$ 233,290	$ 122,456
Net income per share:
Basic (in dollars per share)	$ 2.99	$ 2.60	$ 1.35
Diluted (in dollars per share)	$ 2.96	$ 2.56	$ 1.33
Weighted average shares outstanding:
Basic (in shares)	89,315	89,817	90,827
Diluted (in shares)	90,017	90,971	92,122
Research
Revenues:
Total revenues	$ 3,602,892	$ 3,374,548	$ 3,105,764
Conferences
Revenues:
Total revenues	120,140	476,869	410,461
Consulting
Revenues:
Total revenues	376,371	393,904	353,667
Other
Revenues:
Total revenues	$ 0	$ 0	$ 105,562