STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Collaboration revenue				$ 146
Operating expenses:
Research and development	$ 9,998	$ 7,489	$ 19,474	17,672
General and administrative	4,755	4,889	8,900	11,048
Total operating expenses	14,753	12,378	28,374	28,720
Loss from operations	(14,753)	(12,378)	(28,374)	(28,574)
Other income, net	133	164	320	312
Change in fair value of derivative liabilities		183		211
Net loss	(14,620)	(12,031)	(28,054)	(28,051)
Preferred stock dividends		(5,462)		(10,582)
Net loss applicable to common stockholders	$ (14,620)	$ (17,493)	$ (28,054)	$ (38,633)
Basic and diluted net loss per share	$ (0.09)	$ (0.12)	$ (0.17)	$ (0.27)
Weighted average common shares outstanding used to compute basic and diluted net loss per share	160,789,272	141,017,898	160,718,313	140,935,964

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

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The aggregate costs incurred (1) in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; or (2) to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, including the costs of developing computer software up to the point in time of achieving technological feasibility, and costs allocated in accounting for a business combination to in-process projects deemed to have no alternative future use.

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