STATEMENTS OF OPERATIONS (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenue	$ 1,373us-gaap_ContractsRevenue	$ 800us-gaap_ContractsRevenue	$ 800us-gaap_ContractsRevenue
Operating expenses:
Research and development	32,706us-gaap_ResearchAndDevelopmentExpense	42,852us-gaap_ResearchAndDevelopmentExpense	83,446us-gaap_ResearchAndDevelopmentExpense
General and administrative	12,166us-gaap_GeneralAndAdministrativeExpense	15,661us-gaap_GeneralAndAdministrativeExpense	19,523us-gaap_GeneralAndAdministrativeExpense
Total operating expenses	44,872us-gaap_OperatingCostsAndExpenses	58,513us-gaap_OperatingCostsAndExpenses	102,969us-gaap_OperatingCostsAndExpenses
Loss from operations	(43,499)us-gaap_OperatingIncomeLoss	(57,713)us-gaap_OperatingIncomeLoss	(102,169)us-gaap_OperatingIncomeLoss
Other income (expense), net	(5)us-gaap_OtherNonoperatingIncomeExpense	(579)us-gaap_OtherNonoperatingIncomeExpense	(13)us-gaap_OtherNonoperatingIncomeExpense
Change in fair value of warrants	11,723us-gaap_UnrealizedGainLossOnDerivatives	1,185us-gaap_UnrealizedGainLossOnDerivatives	6,050us-gaap_UnrealizedGainLossOnDerivatives
Net loss	$ (31,781)us-gaap_NetIncomeLoss	$ (57,107)us-gaap_NetIncomeLoss	$ (96,132)us-gaap_NetIncomeLoss
Basic and diluted net loss per share	$ (0.31)us-gaap_EarningsPerShareBasicAndDiluted	$ (0.66)us-gaap_EarningsPerShareBasicAndDiluted	$ (1.22)us-gaap_EarningsPerShareBasicAndDiluted
Weighted average common shares outstanding used to compute basic and diluted net loss per share	101,130,710	85,943,175	78,546,112

Revenue earned during the period arising from products sold or services provided under the terms of a contract, not elsewhere specified in the taxonomy. May include government contracts, construction contracts, and any other contract related to a particular project or product.

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