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Basis of Presentation and Summary of Significant Accounting Policies (Tables)
9 Months Ended
Sep. 30, 2021
Accounting Policies [Abstract]  
Common Stock Equivalents Excluded from Computation of Diluted Net Loss Per Share of Common Stock

 Common Stock Equivalents Excluded from Computation of Diluted Net Loss Per Share of Common Stock

   Three Months Ended   Nine Months Ended 
   September 30,   September 30, 
   2021   2020   2021   2020 
Stock options   4,501    9,256    3,404    8,583 
Warrants   2,555    3,384    2,555    3,384