Information About Reportable Segments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2012	Mar. 31, 2011
Segment Reporting Information [Line Items]
Revenues	$ 369,171	$ 329,567
Gross contribution	224,097	195,655
Corporate and other expenses	(170,541)	(149,874)
Operating income	53,556	45,781
Research
Segment Reporting Information [Line Items]
Revenues	274,620	243,435
Gross contribution	188,602	164,501
Consulting
Segment Reporting Information [Line Items]
Revenues	74,563	70,630
Gross contribution	27,600	25,489
Events
Segment Reporting Information [Line Items]
Revenues	19,988	15,502
Gross contribution	$ 7,895	$ 5,665

Aggregate revenue less cost of goods and services sold or operating expenses directly attributable to the revenue generation activity.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1,2)

-URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688

+ Details

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- Definition

Generally recurring costs associated with normal operations except for the portion of these expenses which can be clearly related to production and included in cost of sales or services. Includes selling, general and administrative expense.

+ References

No definition available.

+ Details

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- Definition

The net result for the period of deducting operating expenses from operating revenues.

+ References

No definition available.

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- Definition

Aggregate revenue recognized during the period (derived from goods sold, services rendered, insurance premiums, or other activities that constitute an entity's earning process). For financial services companies, also includes investment and interest income, and sales and trading gains.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 5

-Section 03

-Paragraph 1

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1)

-URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688

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