Goodwill and Intangible Assets (Detail) - Changes to Carrying Amount of Goodwill by Reporting Unit (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014
Goodwill [Roll Forward]
Balance, December 31, 2013	$ 519,203	[1]
Addition due to acquisition	70,936	[2]
Foreign currency translation adjustments and other	(353)	[2]
Balance, March 31, 2014	589,786
Research
Goodwill [Roll Forward]
Balance, December 31, 2013	376,568	[1]
Addition due to acquisition	70,936	[2]
Foreign currency translation adjustments and other	(306)	[2]
Balance, March 31, 2014	447,198
Consulting
Goodwill [Roll Forward]
Balance, December 31, 2013	100,677	[1]
Addition due to acquisition	0	[2]
Foreign currency translation adjustments and other	(35)	[2]
Balance, March 31, 2014	100,642
Events
Goodwill [Roll Forward]
Balance, December 31, 2013	41,958	[1]
Addition due to acquisition	0	[2]
Foreign currency translation adjustments and other	(12)	[2]
Balance, March 31, 2014	$ 41,946

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

[2] The goodwill resulted from the acquisition of Software Advice (see Note 1 for additional discussion). All of the recorded goodwill from the Software Advice acquisition has been included in the Research segment.