Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Revenues:
Research	$ 1,445,338		$ 1,271,011		$ 1,137,147
Consulting	348,396		314,257		304,893
Events	227,707		198,945		173,768
Total revenues	2,021,441		1,784,213		1,615,808
Costs and expenses:
Cost of services and product development	797,933		713,484		659,067
Selling, general and administrative	876,067		760,458		678,843
Depreciation	31,186		28,996		25,369
Amortization of intangibles	8,226		5,446		4,402
Acquisition and integration charges	21,867		337		2,420
Total costs and expenses	1,735,279		1,508,721		1,370,101
Operating income	286,162		275,492		245,707
Interest income	1,413		1,551		1,046
Interest expense	(12,300)		(10,388)		(9,905)
Other expense, net	(592)		(216)		(1,252)
Income before income taxes	274,683		266,439		235,596
Provision for income taxes	90,917		83,638		69,693
Net income	$ 183,766		$ 182,801		$ 165,903
Net income per share:
Basic (in Dollars per share)	$ 2.06		$ 1.97		$ 1.78
Diluted (in Dollars per share)	$ 2.03		$ 1.93		$ 1.73
Weighted average shares outstanding:
Basic (in shares)	89,337	[1]	93,015	[1]	93,444	[1]
Diluted (in shares)	90,719	[1]	94,830	[1]	95,842	[1]

[1] The Company repurchased 5.9 million, 3.4 million, and 2.7 million shares of its Common Stock in 2014, 2013, and 2012, respectively.