Condensed Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Revenues:
Research	$ 365,334	$ 316,518	$ 1,071,943	$ 938,082
Consulting	82,300	70,149	260,059	228,710
Events	23,306	24,038	105,460	96,714
Total revenues	470,940	410,705	1,437,462	1,263,506
Costs and expenses:
Cost of services and product development	188,059	161,735	562,058	503,376
Selling, general and administrative	217,025	181,546	640,179	547,653
Depreciation	7,945	7,258	23,125	21,375
Amortization of intangibles	2,505	1,351	5,763	4,089
Acquisition and integration charges	6,015	72	16,015	278
Total costs and expenses	421,549	351,962	1,247,140	1,076,771
Operating income	49,391	58,743	190,322	186,735
Interest expense, net	(2,656)	(2,124)	(7,586)	(6,704)
Other (expense) income, net	(287)	5	(341)	(64)
Income before income taxes	46,448	56,624	182,395	179,967
Provision for income taxes	12,602	18,430	57,773	58,584
Net income	$ 33,846	$ 38,194	$ 124,622	$ 121,383
Earnings per common share:
Basic (in Dollars per share)	$ 0.38	$ 0.41	$ 1.39	$ 1.30
Diluted (in Dollars per share)	$ 0.38	$ 0.40	$ 1.37	$ 1.28
Weighted average shares outstanding:
Basic (in shares)	88,513	92,689	89,901	93,286
Diluted (in shares)	89,708	94,355	91,273	95,100