Condensed Statements of Operations and Comprehensive Loss (USD $)
In Thousands, except Share data, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Operating expenses:      
Research and development $ 25,302 $ 16,014 $ 7,998
General and administrative 10,922 6,745 2,206
Total operating expenses 36,224 22,759 10,204
Loss from operations (36,224) (22,759) (10,204)
Interest expense. (270) (936) (1,486)
Change in fair value of warrant liability   (2,587) 32
Other income (expense), net 119 194 (84)
Net loss (36,375) (26,088) (11,742)
Net loss per common share (basic and diluted) (in dollars per share) $ (2.22) $ (3.31) $ (36.31)
Weighted-average shares outstanding (basic and diluted) 16,374,102 7,885,921 323,382
Other comprehensive loss:      
Unrealized loss on investments (56) (3)  
Total comprehensive loss $ (36,431) $ (26,091) $ (11,742)