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Summary of Significant Accounting Policies - Anti-dilutive Securities (Details) - shares
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Stock options    
Anti-dilutive securities    
Anti-dilutive securities (in shares) 46 36
Convertible preferred stock    
Anti-dilutive securities    
Anti-dilutive securities (in shares) 1,288 1,098
Warrants    
Anti-dilutive securities    
Anti-dilutive securities (in shares) 7,142,428 127,540