| Useful Life of Other Purchased Intangible Assets (Detail) | 12 Months Ended | 
|---|---|
| Dec. 31, 2011
 Year | |
| Purchased data files | |
| Finite-Lived Intangible Assets [Line Items] | |
| Useful Life, Minimum | 2 | 
| Useful Life, Maximum | 15 | 
| Acquired software and technology | |
| Finite-Lived Intangible Assets [Line Items] | |
| Useful Life, Minimum | 1 | 
| Useful Life, Maximum | 10 | 
| Non-compete agreements | |
| Finite-Lived Intangible Assets [Line Items] | |
| Useful Life, Minimum | 1 | 
| Useful Life, Maximum | 10 | 
| Proprietary database | |
| Finite-Lived Intangible Assets [Line Items] | |
| Useful Life, Minimum | 6 | 
| Useful Life, Maximum | 10 | 
| Customer relationships | |
| Finite-Lived Intangible Assets [Line Items] | |
| Useful Life, Minimum | 2 | 
| Useful Life, Maximum | 25 | 
| Trade names | |
| Finite-Lived Intangible Assets [Line Items] | |
| Useful Life, Minimum | 5 | 
| Useful Life, Maximum | 15 | 
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- Definition The maximum useful life of a major finite-lived intangible asset class. A major class is composed of intangible assets that can be grouped together because they are similar either by their nature or by their use in the operations of a company. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition The minimum useful life of a major finite-lived intangible asset class. A major class is composed of intangible assets that can be grouped together because they are similar either by their nature or by their use in the operations of a company. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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