Condensed Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Revenues:
Research	$ 396,179	$ 365,334	$ 1,162,987	$ 1,071,943
Consulting	74,686	82,300	239,814	260,059
Events	29,301	23,306	116,487	105,460
Total revenues	500,166	470,940	1,519,288	1,437,462
Costs and expenses:
Cost of services and product development	193,602	188,059	581,859	562,058
Selling, general and administrative	236,355	217,025	703,868	640,179
Depreciation	8,510	7,945	24,939	23,125
Amortization of intangibles	2,737	2,505	6,983	5,763
Acquisition and integration charges	6,488	6,015	15,263	16,015
Total costs and expenses	447,692	421,549	1,332,912	1,247,140
Operating income	52,474	49,391	186,376	190,322
Interest expense, net	(6,049)	(2,656)	(14,769)	(7,586)
Other income (expense), net	5,367	(287)	3,937	(341)
Income before income taxes	51,792	46,448	175,544	182,395
Provision for income taxes	21,426	12,602	65,672	57,773
Net income	$ 30,366	$ 33,846	$ 109,872	$ 124,622
Earnings per common share:
Basic (in Dollars per share)	$ 0.37	$ 0.38	$ 1.30	$ 1.39
Diluted (in Dollars per share)	$ 0.36	$ 0.38	$ 1.29	$ 1.37
Weighted average shares outstanding:
Basic (in shares)	82,989	88,513	84,244	89,901
Diluted (in shares)	84,113	89,708	85,435	91,273