Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues:
Total revenues	$ 3,975,454	$ 3,311,494	$ 2,444,540
Costs and expenses:
Cost of services and product development	1,468,800	1,320,198	945,648
Selling, general and administrative	1,884,141	1,599,004	1,089,184
Depreciation	68,592	63,897	37,172
Amortization of intangibles	187,009	176,274	24,797
Acquisition and integration charges	107,197	158,450	42,598
Total costs and expenses	3,715,739	3,317,823	2,139,399
Operating income (loss)	259,715	(6,329)	305,141
Interest income	2,566	3,011	2,449
Interest expense	(126,774)	(127,947)	(27,565)
Gain from divested operations	45,447	0	0
Other income, net	167	3,448	8,406
Income (loss) before income taxes	181,121	(127,817)	288,431
Provision (benefit) for income taxes	58,665	(131,096)	94,849
Net income	$ 122,456	$ 3,279	$ 193,582
Net income per share:
Basic (in dollars per share)	$ 1.35	$ 0.04	$ 2.34
Diluted (in dollars per share)	$ 1.33	$ 0.04	$ 2.31
Weighted average shares outstanding:
Basic (in shares)	90,827	88,466	82,571
Diluted (in shares)	92,122	89,790	83,820
Research
Revenues:
Total revenues	$ 3,105,764	$ 2,471,280	$ 1,857,001
Conferences
Revenues:
Total revenues	410,461	337,903	268,605
Consulting
Revenues:
Total revenues	353,667	327,661	318,934
Other
Revenues:
Total revenues	$ 105,562	$ 174,650	$ 0