STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Expenses:
Research and development	$ 22,005	$ 18,916	$ 8,690
General and administrative	6,237	5,516	3,230
Loss from operations	(28,242)	(24,432)	(11,920)
Change in fair value of warrant liability			1,192
Interest income	128	64	12
Interest expense	(464)	(475)	(117)
Other expense	(65)	(7)
Net loss	(28,643)	(24,850)	(10,833)
Cumulative preferred stock dividends			(2,545)
Net loss applicable to common stockholders	$ (28,643)	$ (24,850)	$ (13,378)
Per share information:
Net loss per share of common stock-basic and diluted (in dollars per share)	$ (1.47)	$ (1.67)	$ (2.17)
Basic and diluted weighted average shares outstanding (in shares)	19,498,143	14,919,783	6,152,669