Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Schedule of Potentially Dilutive Shares (Details)

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Summary of Significant Accounting Policies - Schedule of Potentially Dilutive Shares (Details) - shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Anti-dilutive securities (in shares) 22,602,545 8,049,365
Outstanding stock options    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Anti-dilutive securities (in shares) 830,343 526,070
Outstanding restricted stock units    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Anti-dilutive securities (in shares) 29,087 96,637
For possible future issuance for the conversion of the March 2019 Notes    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Anti-dilutive securities (in shares) 1,138,200 1,138,200
For possible future issuance for the conversion of the April 2020 Notes    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Anti-dilutive securities (in shares) 1,299,790 0
Warrants to purchase common stock associated with Solar loan agreement | Warrant liability    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Anti-dilutive securities (in shares) 12,243 12,243
Warrants to purchase common stock associated with June 2016 Public Offering | Warrant liability    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Anti-dilutive securities (in shares) 421,867 421,867
March 2018 Public Offering Series 2 [Member] | Warrant liability    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Anti-dilutive securities (in shares) 798,810 798,810
December 2020 Public Offering Series 1 | Warrant liability    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Anti-dilutive securities (in shares) 6,800,000 0
December 2020 Public Offering Series 2 | Warrant liability    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Anti-dilutive securities (in shares) 6,800,000 0
December 2019 Public Offering | Warrant liability    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Anti-dilutive securities (in shares) 4,472,205 4,472,205
December 2019 Public Offering | Option to purchase common stock    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Anti-dilutive securities (in shares) 0 583,333