Consolidated Statements of Operations - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Operating expenses:      
Research and development $ 12,557 $ 10,058 $ 10,273
General and administrative 11,506 12,340 7,566
Total operating expenses 24,063 22,398 17,839
Operating loss (24,063) (22,398) (17,839)
Other income (expense):      
Interest income 187 60 5
Interest expense (155) (172) (136)
Derivatives gain (loss) 593 (10,804) (376)
Other income (expense), net 625 (10,916) (507)
Net loss $ (23,438) $ (33,314) $ (18,346)
Net loss per share, basic and diluted (in dollars per share) $ (0.76) $ (1.26) $ (0.83)
Weighted average number of common shares outstanding, basic and diluted 31,025,585 26,461,374 22,080,761