Changes to the Carrying Amount of Goodwill by Reporting Segments (Detail) (USD $) In Thousands	9 Months Ended
	Sep. 30, 2011
Goodwill [Line Items]
Beginning Balance	$ 510,265	[1]
Foreign currency translation adjustments	(38)
Ending Balance	510,227
Research
Goodwill [Line Items]
Beginning Balance	368,521	[1]
Foreign currency translation adjustments	(69)
Ending Balance	368,452
Consulting
Goodwill [Line Items]
Beginning Balance	99,817	[1]
Foreign currency translation adjustments	17
Ending Balance	99,834
Events
Goodwill [Line Items]
Beginning Balance	41,927	[1]
Foreign currency translation adjustments	14
Ending Balance	$ 41,941

[1] The Company does not have any accumulated goodwill impairment losses.