Condensed Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Revenues:
Research	$ 278,302	$ 250,015	$ 552,922	$ 493,450
Consulting	76,676	77,962	151,239	148,592
Events	42,504	37,566	62,492	53,068
Total revenues	397,482	365,543	766,653	695,110
Costs and expenses:
Cost of services and product development	161,247	152,461	307,710	285,777
Selling, general and administrative	165,221	152,758	327,739	294,430
Depreciation	6,182	6,234	12,077	12,505
Amortization of intangibles	928	2,522	1,667	5,049
Acquisition and integration charges	1,182		1,182
Total costs and expenses	334,760	313,975	650,375	597,761
Operating income	62,722	51,568	116,278	97,349
Interest expense, net	(2,153)	(2,797)	(4,348)	(5,581)
Other expense, net	(76)	(571)	(1,054)	(953)
Income before income taxes	60,493	48,200	110,876	90,815
Provision for income taxes	19,009	15,977	35,171	29,401
Net income	$ 41,484	$ 32,223	$ 75,705	$ 61,414
Income per common share:
Basic	$ 0.44	$ 0.33	$ 0.81	$ 0.64
Diluted	$ 0.43	$ 0.32	$ 0.79	$ 0.62
Weighted average shares outstanding:
Basic	93,350	96,886	93,383	96,664
Diluted	95,423	99,340	95,826	99,642