Information About Reportable Segments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Segment Reporting Information [Line Items]
Revenues	$ 397,482	$ 365,543	$ 766,653	$ 695,110
Gross contribution	237,771	214,492	461,869	410,147
Corporate and other expenses	(175,049)	(162,924)	(345,591)	(312,798)
Operating income	62,722	51,568	116,278	97,349
Research
Segment Reporting Information [Line Items]
Revenues	278,302	250,015	552,922	493,450
Gross contribution	189,471	168,304	378,074	332,805
Consulting
Segment Reporting Information [Line Items]
Revenues	76,676	77,962	151,239	148,592
Gross contribution	27,906	28,873	55,506	54,362
Events
Segment Reporting Information [Line Items]
Revenues	42,504	37,566	62,492	53,068
Gross contribution	$ 20,394	$ 17,315	$ 28,289	$ 22,980

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

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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.

+ Details

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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 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

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

+ Details

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- Details

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