Business and Significant Accounting Policies (Detail) - Changes to the Carrying Amount of Goodwill by Reporting Unit (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Goodwill [Roll Forward]
Beginning Balance	$ 519,506		$ 508,550	[1]
Addition due to acquisition	7,455	[2]
Foreign currency translation adjustments	(303)		3,501
Ending Balance	519,203		519,506
Research
Goodwill [Roll Forward]
Beginning Balance	377,225		366,980	[1]
Addition due to acquisition					7,455	[2]
Foreign currency translation adjustments	(657)		2,790
Ending Balance	376,568		377,225		366,980	[1]
Consulting
Goodwill [Roll Forward]
Beginning Balance	100,349		99,677	[1]
Addition due to acquisition	0	[2]
Foreign currency translation adjustments	328		672
Ending Balance	100,677		100,349
Events
Goodwill [Roll Forward]
Beginning Balance	41,932		41,893	[1]
Addition due to acquisition	0	[2]
Foreign currency translation adjustments	26		39
Ending Balance	$ 41,958		$ 41,932

[1] The Company does not have an accumulated goodwill impairment loss.

[2] The additions are from the Company's acquisition of Ideas International. See Acquisitions above for additional information.