Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Revenues:
Research	$ 449,170	$ 385,718	$ 889,441	$ 766,808
Consulting	94,068	88,336	179,008	165,128
Events	66,760	73,882	98,815	87,186
Total revenues	609,998	547,936	1,167,264	1,019,122
Costs and expenses:
Cost of services and product development	231,422	210,495	443,463	388,257
Selling, general and administrative	272,009	237,991	529,420	467,513
Depreciation	9,025	8,440	17,859	16,429
Amortization of intangibles	6,210	2,107	12,393	4,246
Acquisition and integration charges	8,033	3,683	16,401	8,775
Total costs and expenses	526,699	462,716	1,019,536	885,220
Operating income	83,299	85,220	147,728	133,902
Interest expense, net	(7,356)	(5,240)	(13,362)	(8,720)
Other income (expense), net	1,248	(468)	3,132	(1,430)
Income before income taxes	77,191	79,512	137,498	123,752
Provision for income taxes	29,280	28,357	49,420	44,246
Net income	$ 47,911	$ 51,155	$ 88,078	$ 79,506
Net income per share:
Basic (in dollars per share)	$ 0.58	$ 0.61	$ 1.07	$ 0.94
Diluted (in dollars per share)	$ 0.57	$ 0.61	$ 1.05	$ 0.92
Weighted average shares outstanding:
Basic (in shares)	82,559	83,203	82,505	84,871
Diluted (in shares)	83,476	84,271	83,498	86,064