Marketable Securities and Fair Value Measurements Additional Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Investments, Debt and Equity Securities [Abstract]
Asset Impairment Charges	$ 26,320	$ 0
Impairment of goodwill	$ 40,693	$ 0
Maturity Period Used To Classify Investments			2 years
Marketable Securities, Weighted Average Remaining Maturity	6 months		10 months

The charge against earnings resulting from the aggregate write down of all assets from their carrying value to their fair value.

+ References+ Details

Loss recognized during the period that results from the write-down of goodwill after comparing the implied fair value of reporting unit goodwill with the carrying amount of that goodwill. Goodwill is assessed at least annually for impairment.

+ References

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+ Details