Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenues:
Total revenues	$ 1,070,882	$ 1,001,336	$ 2,041,326	$ 1,964,901
Costs and expenses:
Cost of services and product development	387,999	367,637	734,644	724,846
Selling, general and administrative	514,976	460,803	1,033,746	948,548
Depreciation	20,099	16,711	39,874	33,121
Amortization of intangibles	32,164	50,127	65,847	101,773
Acquisition and integration charges (credits)	(358)	19,962	2,414	79,228
Total costs and expenses	954,880	915,240	1,876,525	1,887,516
Operating income	116,002	86,096	164,801	77,385
Interest expense, net	(24,749)	(37,604)	(49,596)	(72,663)
Gain (loss) from divested operations	0	25,460	(2,075)	25,460
Other (expense) income, net	(247)	1,120	(1,071)	2,019
Income before income taxes	91,006	75,072	112,059	32,201
(Benefit) provision for income taxes	(12,400)	28,802	(12,142)	5,518
Net income	$ 103,406	$ 46,270	$ 124,201	$ 26,683
Net income per share:
Basic (in dollars per share)	$ 1.15	$ 0.51	$ 1.38	$ 0.29
Diluted (in dollars per share)	$ 1.13	$ 0.50	$ 1.36	$ 0.29
Weighted average shares outstanding:
Basic (in shares)	90,112	91,048	89,997	91,026
Diluted (in shares)	91,188	92,156	91,146	92,252
Research
Revenues:
Total revenues	$ 826,055	$ 770,314	$ 1,651,429	$ 1,534,238
Conferences
Revenues:
Total revenues	141,174	111,253	193,106	157,340
Consulting
Revenues:
Total revenues	103,653	96,458	196,791	179,354
Other
Revenues:
Total revenues	$ 0	$ 23,311	$ 0	$ 93,969