Condensed Statements of Operations and Comprehensive Loss - USD ($)
 3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Operating expenses:        
Research and development $ 3,073,344 $ 1,243,221 $ 4,271,659 $ 7,601,225
General and administrative 3,049,711 2,132,850 6,164,206 7,103,463
Total operating expenses 6,123,055 3,376,071 10,435,865 14,704,688
Loss from operations (6,123,055) (3,376,071) (10,435,865) (14,704,688)
Other income (expense):        
Interest income 72,641 54,637 99,097 85,129
Interest expense (431,626) (894,118) (858,871) (4,555,737)
Loss on extinguishment of convertible note payable 0 0 (1,049,166) 0
Change in fair value of derivative liability and extinguishment of derivative liability 181,000 0 652,000 0
Change in fair value of warrant liabilities 1,812,800 0 2,669,800 0
Total other income (expense), net 1,634,815 (839,481) 1,512,860 (4,470,608)
Loss before income taxes (4,488,240) (4,215,552) (8,923,005) (19,175,296)
Benefit from income taxes 0 0 0 0
Net loss $ (4,488,240) $ (4,215,552) $ (8,923,005) $ (19,175,296)
Net loss per common share, basic and diluted (in usd per share) $ (0.13) $ (0.16) $ (0.29) $ (0.82)
Weighted-average common shares, basic and diluted (in shares) 33,973,788 25,695,171 30,631,601 23,481,834