Goodwill and Intangible Assets (Detail) - Changes to Carrying Amount of Goodwill by Reporting Unit (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012
Balance, December 31, 2011	$ 508,550
Addition due to acquisition (1)	7,455	[1]
Foreign currency translation adjustments	3,195
Balance, September 30, 2012 (2)	519,200	[2]
Research [Member]
Balance, December 31, 2011	366,980
Addition due to acquisition (1)	7,455	[1]
Foreign currency translation adjustments	2,488
Balance, September 30, 2012 (2)	376,923	[2]
Consulting And Product Support Services [Member]
Balance, December 31, 2011	99,677
Foreign currency translation adjustments	683
Balance, September 30, 2012 (2)	100,360	[2]
Operating Segments [Member]
Balance, December 31, 2011	41,893
Foreign currency translation adjustments	24
Balance, September 30, 2012 (2)	41,917	[2]
Ideas International Limited [Member]
Addition due to acquisition (1)	$ 7,500

[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.