Amount of debt securities categorized neither as held-to-maturity nor trading.

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+ Details

Fair Value Hierarchy (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Assets
Money market funds(1)	$ 57,918	$ 2,062
U.S. government bonds and notes(2)	22,052
Total available-for-sale debt securities	79,970
Liabilities
Convertible preferred stock warrants(2)		(1,137)
Level 1 [Member]
Assets
Money market funds(1)	57,918	2,062
U.S. government bonds and notes(2)	22,052
Total available-for-sale debt securities	79,970
Liabilities
Convertible preferred stock warrants(2)
Level 2 [Member]
Assets
Money market funds(1)
U.S. government bonds and notes(2)
Total available-for-sale debt securities
Liabilities
Convertible preferred stock warrants(2)
Level 3 [Member]
Assets
Money market funds(1)
U.S. government bonds and notes(2)
Total available-for-sale debt securities
Liabilities
Convertible preferred stock warrants(2)		$ (1,137)