Annual report pursuant to Section 13 and 15(d)

Net Loss Per Common Share - Anti-Dilutive Securities (Details)

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Net Loss Per Common Share - Anti-Dilutive Securities (Details) - shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Antidilutive securities excluded from computation of earnings per share (in shares) 16,176,000 9,513,000 12,852,000
Stock options      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Antidilutive securities excluded from computation of earnings per share (in shares) 14,486,000 7,822,000 7,591,000
Warrants      
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]      
Antidilutive securities excluded from computation of earnings per share (in shares) 1,690,000 1,691,000 5,261,000