Annual report pursuant to Section 13 and 15(d)

Stockholders' Equity - Fair Value of Warrants Issued Using the Black-Scholes-Merton Option (Details)

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Stockholders' Equity - Fair Value of Warrants Issued Using the Black-Scholes-Merton Option (Details) - USD ($)
$ / shares in Units, $ in Thousands
Jul. 31, 2016
Apr. 30, 2016
Jan. 31, 2016
Dec. 31, 2019
May 24, 2016
Class of Stock [Line Items]          
Warrant shares issued (in shares)       807,436  
Share price (in dollars per share)         $ 11.39
Veolia Warrant #1          
Class of Stock [Line Items]          
Warrant shares issued (in shares)     2,000,000    
Share price (in dollars per share)     $ 3.02    
Warrant exercise price (in dollars per share)     $ 5.00    
Term     10 years    
Risk free interest rate     2.64%    
Volatility     81.50%    
Dividend rate     0.00%    
Per share FV of warrant (in usd per share)     $ 2.35    
FV of warrant     $ 4,699    
Veolia Warrant #2          
Class of Stock [Line Items]          
Warrant shares issued (in shares)   2,000,000      
Share price (in dollars per share)   $ 3.02      
Warrant exercise price (in dollars per share)   $ 7.00      
Term   10 years      
Risk free interest rate   2.64%      
Volatility   81.50%      
Dividend rate   0.00%      
Per share FV of warrant (in usd per share)   $ 2.24      
FV of warrant   $ 4,474      
Jan. 2019 Offering Underwriter          
Class of Stock [Line Items]          
Warrant shares issued (in shares) 103,500        
Share price (in dollars per share) $ 2.16        
Warrant exercise price (in dollars per share) $ 1.90        
Term 5 years        
Risk free interest rate 2.57%        
Volatility 81.00%        
Dividend rate 0.00%        
Per share FV of warrant (in usd per share) $ 1.47        
FV of warrant $ 152