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

v3.20.1
Fair Value of Warrants - Assumptions Used in Computing Fair Value of Derivative Warrants (Details) - $ / shares
3 Months Ended 12 Months Ended
Mar. 31, 2020
Dec. 31, 2019
Class of Warrant or Right [Line Items]    
Exercise price (usd per share) $ 104.18  
2016 Offering    
Class of Warrant or Right [Line Items]    
Exercise price (usd per share) $ 67.50 $ 67.50
Expected life (years) 1 year 9 months 29 days 2 years 29 days
Expected volatility | 2016 Offering    
Class of Warrant or Right [Line Items]    
Measurement input assumption (as a percent) 157.00% 150.69%
Risk-free interest rate | 2016 Offering    
Class of Warrant or Right [Line Items]    
Measurement input assumption (as a percent) 0.23% 1.58%
Expected dividend yield | 2016 Offering    
Class of Warrant or Right [Line Items]    
Measurement input assumption (as a percent) 0.00% 0.00%