Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues:
Total revenues	$ 1,001,336	$ 843,731	$ 1,964,901	$ 1,468,900
Costs and expenses:
Cost of services and product development	367,637	352,004	724,846	589,613
Selling, general and administrative	460,803	408,226	948,548	712,470
Depreciation	16,711	18,057	33,121	28,297
Amortization of intangibles	50,127	65,500	101,773	71,790
Acquisition and integration charges	19,962	98,332	79,228	111,604
Total costs and expenses	915,240	942,119	1,887,516	1,513,774
Operating income (loss)	86,096	(98,388)	77,385	(44,874)
Interest expense, net	(37,604)	(43,956)	(72,663)	(49,862)
Gain from divested operations	25,460	0	25,460	0
Other income (expense), net	1,120	(407)	2,019	482
Income (loss) before income taxes	75,072	(142,751)	32,201	(94,254)
Provision (benefit) for income taxes	28,802	(50,470)	5,518	(38,406)
Net income (loss)	$ 46,270	$ (92,281)	$ 26,683	$ (55,848)
Net income (loss) per share:
Basic (in dollars per share)	$ 0.51	$ (1.03)	$ 0.29	$ (0.65)
Diluted (in dollars per share)	$ 0.50	$ (1.03)	$ 0.29	$ (0.65)
Weighted average shares outstanding:
Basic (in shares)	91,048	89,297	91,026	86,066
Diluted (in shares)	92,156	89,297	92,252	86,066
Research
Revenues:
Total revenues	$ 770,314	$ 613,732	$ 1,534,238	$ 1,125,038
Events
Revenues:
Total revenues	111,253	91,205	157,340	126,474
Consulting
Revenues:
Total revenues	96,458	91,693	179,354	170,287
Other
Revenues:
Total revenues	$ 23,311	$ 47,101	$ 93,969	$ 47,101