Condensed Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Revenues:
Research	$ 348,114	$ 310,331
Consulting	84,271	72,633
Events	14,317	23,790
Total revenues	446,702	406,754
Costs and expenses:
Cost of services and product development	170,821	163,737
Selling, general and administrative	204,617	180,478
Depreciation	7,459	7,100
Amortization of intangibles	1,279	1,334
Acquisition and integration charges	3,356	100
Total costs and expenses	387,532	352,749
Operating income	59,170	54,005
Interest expense, net	(2,250)	(2,436)
Other (expense) income, net	(229)	211
Income before income taxes	56,691	51,780
Provision for income taxes	18,955	15,105
Net income	$ 37,736	$ 36,675
Earnings per common share:
Basic (in Dollars per share)	$ 0.41	$ 0.39
Diluted (in Dollars per share)	$ 0.40	$ 0.38
Weighted average shares outstanding:
Basic (in shares)	91,669	93,595
Diluted (in shares)	93,209	95,537