Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Revenues:
Research	$ 461,502	$ 396,179	$ 1,350,943	$ 1,162,987
Consulting	79,082	74,686	258,090	239,814
Events	33,475	29,301	132,290	116,487
Total revenues	574,059	500,166	1,741,323	1,519,288
Costs and expenses:
Cost of services and product development	223,122	193,602	666,585	581,859
Selling, general and administrative	269,902	236,355	799,322	703,868
Depreciation	9,531	8,510	27,390	24,939
Amortization of intangibles	6,221	2,737	18,614	6,983
Acquisition and integration charges	16,557	6,488	32,958	15,263
Total costs and expenses	525,333	447,692	1,544,869	1,332,912
Operating income	48,726	52,474	196,454	186,376
Interest expense, net	(5,932)	(6,049)	(19,294)	(14,769)
Other income, net	1,954	5,367	5,086	3,937
Income before income taxes	44,748	51,792	182,246	175,544
Provision for income taxes	14,264	21,426	55,149	65,672
Net income	$ 30,484	$ 30,366	$ 127,097	$ 109,872
Net income per share:
Basic (in dollars per share)	$ 0.37	$ 0.37	$ 1.54	$ 1.30
Diluted (in dollars per share)	$ 0.36	$ 0.36	$ 1.52	$ 1.29
Weighted average shares outstanding:
Basic (in shares)	82,638	82,989	82,549	84,244
Diluted (in shares)	83,803	84,113	83,761	85,435