Condensed Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Revenues:
Research	$ 358,495	$ 311,233	$ 706,609	$ 621,564
Consulting	93,488	85,928	177,759	158,561
Events	67,837	48,886	82,154	72,676
Total revenues	519,820	446,047	966,522	852,801
Costs and expenses:
Cost of services and product development	203,178	177,904	373,999	341,641
Selling, general and administrative	218,537	185,629	423,154	366,107
Depreciation	7,721	7,017	15,180	14,117
Amortization of intangibles	1,979	1,404	3,258	2,738
Acquisition and integration charges	6,644	106	10,000	206
Total costs and expenses	438,059	372,060	825,591	724,809
Operating income	81,761	73,987	140,931	127,992
Interest expense, net	(2,680)	(2,144)	(4,930)	(4,580)
Other income (expense), net	175	(280)	(54)	(69)
Income before income taxes	79,256	71,563	135,947	123,343
Provision for income taxes	26,216	25,049	45,171	40,154
Net income	$ 53,040	$ 46,514	$ 90,776	$ 83,189
Earnings per common share:
Basic (in Dollars per share)	$ 0.59	$ 0.50	$ 1.00	$ 0.89
Diluted (in Dollars per share)	$ 0.58	$ 0.49	$ 0.99	$ 0.87
Weighted average shares outstanding:
Basic (in shares)	89,521	93,574	90,595	93,584
Diluted (in shares)	90,744	95,188	92,012	95,426