Quarterly report pursuant to Section 13 or 15(d)

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

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Fair Value of Warrants - Assumptions Used in Computing Fair Value of Derivative Warrants (Details)
3 Months Ended 9 Months Ended
Sep. 30, 2017
$ / shares
Sep. 30, 2017
$ / shares
Sep. 30, 2018
$ / shares
Dec. 31, 2017
$ / shares
2017 Debt        
Class of Warrant or Right [Line Items]        
Exercise price (in dollars per share) $ 2.82 $ 2.82 $ 2.82 $ 2.82
Expected life (years) 7 years 7 years 5 years 11 months 20 days 6 years 2 months 19 days
2017 Offering        
Class of Warrant or Right [Line Items]        
Exercise price (in dollars per share) $ 2.82 $ 2.82 $ 2.36 $ 2.36
Expected life (years) 7 years 7 years 8 months 10 days 1 year 5 months 5 days
2016 Offering        
Class of Warrant or Right [Line Items]        
Exercise price (in dollars per share)     $ 2.25 $ 2.25
Exercise price (in dollars per share) $ 2.25 $ 2.25    
Expected life (years)     3 years 3 months 29 days 4 years 29 days
Expected life (years) 4 years 3 months 18 days 4 years 9 months 11 days    
Expected volatility | 2017 Debt        
Class of Warrant or Right [Line Items]        
Measurement input assumption 0.7461 0.7461 0.7340 0.7418
Expected volatility | 2017 Offering        
Class of Warrant or Right [Line Items]        
Measurement input assumption 0.7461 0.7461 0.9326 0.7755
Expected volatility | 2016 Offering        
Class of Warrant or Right [Line Items]        
Measurement input assumption     0.8088 0.7344
Measurement input assumption 74.20% 76.24%    
Risk-free interest rate | 2017 Debt        
Class of Warrant or Right [Line Items]        
Measurement input assumption 0.0222 0.0222 0.0000 0.0233
Risk-free interest rate | 2017 Offering        
Class of Warrant or Right [Line Items]        
Measurement input assumption 0.0222 0.0222 0.0236 0.0183
Risk-free interest rate | 2016 Offering        
Class of Warrant or Right [Line Items]        
Measurement input assumption     0.0288 0.0211
Measurement input assumption 1.81% 1.94%    
Expected dividend yield | 2017 Debt        
Class of Warrant or Right [Line Items]        
Measurement input assumption 0.0000 0.0000 0.0255 0.0000
Expected dividend yield | 2017 Offering        
Class of Warrant or Right [Line Items]        
Measurement input assumption 0.0000 0.0000 0.0000 0.0000
Expected dividend yield | 2016 Offering        
Class of Warrant or Right [Line Items]        
Measurement input assumption     0.0000 0.0000
Measurement input assumption 0.00% 0.00%