Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues:
Total revenues	$ 921,674	$ 828,085	$ 2,886,575	$ 2,296,985
Costs and expenses:
Cost of services and product development	336,112	332,207	1,060,958	921,820
Selling, general and administrative	447,537	421,163	1,396,085	1,133,633
Depreciation	17,335	17,340	50,456	45,637
Amortization of intangibles	50,852	51,224	152,625	123,014
Acquisition and integration charges	17,114	30,500	96,342	142,104
Total costs and expenses	868,950	852,434	2,756,466	2,366,208
Operating income (loss)	52,724	(24,349)	130,109	(69,223)
Interest expense, net	(26,984)	(38,762)	(99,647)	(88,624)
Gain from divested operations	13,040	0	38,500	0
Other (expense) income, net	(827)	1,171	1,193	1,653
Income (loss) before income taxes	37,953	(61,940)	70,155	(156,194)
Provision (benefit) for income taxes	26,200	(13,760)	31,719	(52,166)
Net income (loss)	$ 11,753	$ (48,180)	$ 38,436	$ (104,028)
Net income (loss) per share:
Basic (in dollars per share)	$ 0.13	$ (0.53)	$ 0.42	$ (1.19)
Diluted (in dollars per share)	$ 0.13	$ (0.53)	$ 0.42	$ (1.19)
Weighted average shares outstanding:
Basic (in shares)	90,854	90,624	90,969	87,585
Diluted (in shares)	92,148	90,624	92,244	87,585
Research
Revenues:
Total revenues	$ 774,188	$ 653,443	$ 2,308,426	$ 1,778,481
Events
Revenues:
Total revenues	57,141	44,953	214,481	171,427
Consulting
Revenues:
Total revenues	78,752	72,117	258,106	242,404
Other
Revenues:
Total revenues	$ 11,593	$ 57,572	$ 105,562	$ 104,673