| Goodwill and Intangible Assets - Additional Information (Detail) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
| Sep. 30, 2012 | Sep. 30, 2011 | Sep. 30, 2012 | Sep. 30, 2011 | |
| Goodwill and Intangible Assets Disclosure [Line Items] | ||||
| Amortization expense related to purchased intangible assets | $ 22.1 | $ 21.9 | $ 66.8 | $ 67.9 | 
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- Definition The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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