Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenues:
Total revenues	$ 973,135	$ 1,070,882	$ 1,992,026	$ 2,041,326
Costs and expenses:
Cost of services and product development	322,551	387,999	663,829	734,644
Selling, general and administrative	494,840	514,976	991,479	1,033,746
Depreciation	22,728	20,099	45,245	39,874
Amortization of intangibles	31,208	32,164	63,387	65,847
Acquisition and integration charges (credits)	2,157	(358)	3,716	2,414
Total costs and expenses	873,484	954,880	1,767,656	1,876,525
Operating income	99,651	116,002	224,370	164,801
Interest expense, net	(30,296)	(24,749)	(56,644)	(49,596)
Loss from divested operations	0	0	0	(2,075)
Other expense, net	(10,399)	(247)	(11,915)	(1,071)
Income before income taxes	58,956	91,006	155,811	112,059
Provision (benefit) for income taxes	3,879	(12,400)	25,637	(12,142)
Net income	$ 55,077	$ 103,406	$ 130,174	$ 124,201
Net income per share:
Basic (in dollars per share)	$ 0.62	$ 1.15	$ 1.46	$ 1.38
Diluted (in dollars per share)	$ 0.61	$ 1.13	$ 1.45	$ 1.36
Weighted average shares outstanding:
Basic (in shares)	89,323	90,112	89,271	89,997
Diluted (in shares)	89,780	91,188	89,967	91,146
Research
Revenues:
Total revenues	$ 875,329	$ 826,055	$ 1,784,620	$ 1,651,429
Conferences
Revenues:
Total revenues	317	141,174	14,187	193,106
Consulting
Revenues:
Total revenues	$ 97,489	$ 103,653	$ 193,219	$ 196,791