Cash Equivalents and Investments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Carrying value of company's non-marketable equity securities	$ 42.1	$ 43.9
Gain Recognized from re-measurement of pre-acquisition equity interest to estimated fair value	5.8
Pre-tax gain on sale of certain non-marketable securities	2.6		4.8
Sale of non-marketable securities		0
Number of investments in an unrealized loss position	99
Impairment charge for certain marketable equity securities	$ 0	$ 0.2	$ 0

Disclosure regarding factors used to determine that the impairment of securities not categorized as either held-to-maturity securities or trading securities (hence equal to available for sale securities) where cost exceeds fair value is not an other than temporary impairment (OTTI). This item contains disclosure of the number of investment positions in the available-for-sale investments determined to be temporarily impaired.

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The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

+ References

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

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+ Details

- Definition

Total debt and equity financial instruments including: (1) securities held-to-maturity, (2) trading securities, and (3) securities available-for-sale.

+ References+ Details