Segments and Geographic Areas - Summary Of Revenues, Adjusted Revenues, Adjusted Segment EBITDA And Adjusted EBITDA Margin For Company's Reportable Segments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenue
Total revenue	$ 193,720	$ 164,749	$ 135,718	$ 128,467	$ 131,951	$ 121,607	$ 117,482	$ 113,623	$ 622,654	$ 484,663	$ 432,431
Adjusted revenue
Total Adjusted revenue									639,788	484,663	432,431
Adjusted EBITDA
Total Adjusted EBITDA									174,189	120,757	110,058
Adjusted EBITDA margin
Total Adjusted EBITDA margin									27.20%	24.90%	25.50%
Depreciation and amortization
Total depreciation and amortization									37,858	16,928	18,039
CEB [Member]
Revenue
Total revenue									564,062	484,663	432,431
Adjusted revenue
Total Adjusted revenue									564,062	484,663	432,431
Adjusted EBITDA
Total Adjusted EBITDA									154,600	120,757	110,058
Adjusted EBITDA margin
Total Adjusted EBITDA margin									27.40%	24.90%	25.50%
Depreciation and amortization
Total depreciation and amortization									24,371	16,928	18,039
SHL [Member]
Revenue
Total revenue									58,592
Adjusted revenue
Total Adjusted revenue									75,726
Adjusted EBITDA
Total Adjusted EBITDA									19,589
Adjusted EBITDA margin
Total Adjusted EBITDA margin									25.90%
Depreciation and amortization
Total depreciation and amortization									$ 13,487