Changes To Carrying Amount Of Goodwill By Reporting Unit (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012
Goodwill [Line Items]
Beginning Balance	$ 508,550
Foreign currency translation adjustments	2,383
Ending Balance	510,933	[1]
Research
Goodwill [Line Items]
Beginning Balance	366,980
Foreign currency translation adjustments	1,940
Ending Balance	368,920	[1]
Consulting
Goodwill [Line Items]
Beginning Balance	99,677
Foreign currency translation adjustments	410
Ending Balance	100,087	[1]
Events
Goodwill [Line Items]
Beginning Balance	41,893
Foreign currency translation adjustments	33
Ending Balance	$ 41,926	[1]

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