Segment Information (Detail) - Information About Reportable Segments (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenues	$ 1,615,808	$ 1,468,588	$ 1,288,454
Gross contribution	963,714	863,239	742,296
Corporate and other expenses	(718,007)	(649,177)	(593,031)
Operating income	245,707	214,062	149,265
Research [Member]
Revenues	1,137,147	1,012,062	865,000
Gross contribution	774,342	682,136	564,527
Consulting [Member]
Revenues	304,893	308,047	302,117
Gross contribution	109,253	114,838	121,885
Events [Member]
Revenues	173,768	148,479	121,337
Gross contribution	$ 80,119	$ 66,265	$ 55,884

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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