Condensed Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Revenues:
Research	$ 284,048	$ 255,979	$ 836,970	$ 749,429
Consulting	71,731	70,815	222,970	219,407
Events	18,627	18,990	81,119	72,058
Total revenues	374,406	345,784	1,141,059	1,040,894
Costs and expenses:
Cost of services and product development	151,143	142,696	458,853	428,473
Selling, general and administrative	164,888	148,461	492,627	442,891
Depreciation	6,301	6,638	18,378	19,143
Amortization of intangibles	1,362	739	3,029	5,788
Acquisition and integration charges	944		2,126
Total costs and expenses	324,638	298,534	975,013	896,295
Operating income	49,768	47,250	166,046	144,599
Interest expense, net	(2,209)	(2,282)	(6,557)	(7,863)
Other expense, net	(748)	(541)	(1,802)	(1,494)
Income before income taxes	46,811	44,427	157,687	135,242
Provision for income taxes	15,436	13,963	50,607	43,364
Net income	$ 31,375	$ 30,464	$ 107,080	$ 91,878
Income per common share:
Basic (in Dollars per share)	$ 0.34	$ 0.32	$ 1.15	$ 0.95
Diluted (in Dollars per share)	$ 0.33	$ 0.31	$ 1.12	$ 0.92
Weighted average shares outstanding:
Basic (in Shares)	93,522	96,057	93,429	96,462
Diluted (in Shares)	95,611	98,259	95,791	99,467