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Stockholders' Equity - Pre-Funded Series D Warrant Exercises - Additional Information (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 21, 2018
Stockholders Equity Note [Line Items]      
Warrants exercised 4,574,529 246  
Pre-Funded Series D Warrants [Member]      
Stockholders Equity Note [Line Items]      
Warrants exercised 3.7    
Pre-Funded Series D Warrants [Member] | Maximum [Member]      
Stockholders Equity Note [Line Items]      
Maximum offering and selling of stock and securities that entity make to raise capital     $ 100.0