Quarterly report pursuant to Section 13 or 15(d)

Fair Value of Warrants - Assumptions Used in Computing Fair Value of Derivative Warrants (Details)

v3.19.2
Fair Value of Warrants - Assumptions Used in Computing Fair Value of Derivative Warrants (Details) - $ / shares
6 Months Ended 12 Months Ended
Jun. 30, 2019
Dec. 31, 2018
Jan. 14, 2019
Jan. 09, 2019
Class of Warrant or Right [Line Items]        
Exercise price (usd per share)     $ 0.2475 $ 0.2475
2016 Offering        
Class of Warrant or Right [Line Items]        
Exercise price (usd per share) $ 2.25 $ 2.25    
Expected life (years) 2 years 6 months 29 days 3 years 29 days    
2017 Offering        
Class of Warrant or Right [Line Items]        
Exercise price (usd per share)   $ 2.36    
Expected life (years)   5 months 9 days    
Expected volatility | 2016 Offering        
Class of Warrant or Right [Line Items]        
Measurement input assumption (as a percent) 114.13% 100.51%    
Expected volatility | 2017 Offering        
Class of Warrant or Right [Line Items]        
Measurement input assumption (as a percent)   172.50%    
Risk-free interest rate | 2016 Offering        
Class of Warrant or Right [Line Items]        
Measurement input assumption (as a percent) 1.73% 2.46%    
Risk-free interest rate | 2017 Offering        
Class of Warrant or Right [Line Items]        
Measurement input assumption (as a percent)   2.56%    
Expected dividend yield | 2016 Offering        
Class of Warrant or Right [Line Items]        
Measurement input assumption (as a percent) 0.00% 0.00%    
Expected dividend yield | 2017 Offering        
Class of Warrant or Right [Line Items]        
Measurement input assumption (as a percent)   0.00%