Changes to Carrying Amount of Goodwill by Reporting Unit (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012
Goodwill [Line Items]
Beginning Balance	$ 508,550
Addition due to acquisition	7,455	[1]
Foreign currency translation adjustments	(1,003)
Ending Balance	515,002	[2]
Research
Goodwill [Line Items]
Beginning Balance	366,980
Addition due to acquisition	7,455	[1]
Foreign currency translation adjustments	(1,005)
Ending Balance	373,430	[2]
Consulting
Goodwill [Line Items]
Beginning Balance	99,677
Foreign currency translation adjustments	34
Ending Balance	99,711	[2]
Events
Goodwill [Line Items]
Beginning Balance	41,893
Foreign currency translation adjustments	(32)
Ending Balance	$ 41,861	[2]

[1] The Company acquired Ideas International in the second quarter of 2012 and recorded $7.5 million of goodwill. All of the recorded goodwill resulting from the acquisition has been included in the Research segment. See Note 2-Acquisition above for additional information.

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