Quarterly report pursuant to Section 13 or 15(d)

Common Stock Warrants (Details)

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Common Stock Warrants (Details) - $ / shares
Jun. 30, 2020
Dec. 31, 2019
Mar. 31, 2019
May 31, 2018
Feb. 29, 2016
Feb. 28, 2015
Warrants            
Aggregate number of unregistered shares of common stock called by warrants (in shares) 19,426 28,489        
Common stock warrant, Exercise price $66.20 per share, Issued February 2015            
Warrants            
Exercise price of warrants (in dollars per share)           $ 66.20
Aggregate number of unregistered shares of common stock called by warrants (in shares)           9,063
Common stock warrant, Exercise Price $15.40 per share, Issued February 2016            
Warrants            
Exercise price of warrants (in dollars per share)         $ 15.40  
Aggregate number of unregistered shares of common stock called by warrants (in shares)         8,249  
Common stock warrant, Exercise price $23.69 per share, Issued May 2018            
Warrants            
Exercise price of warrants (in dollars per share)       $ 23.69    
Aggregate number of unregistered shares of common stock called by warrants (in shares)       6,332    
Common stock warrant, Exercise price $14.71 per share, Issued March 2019            
Warrants            
Exercise price of warrants (in dollars per share)     $ 14.71      
Aggregate number of unregistered shares of common stock called by warrants (in shares)     4,845