Quarterly report pursuant to Section 13 or 15(d)

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

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Summary of Significant Accounting Policies - Schedule of Potentially Dilutive Shares (Detail) - shares
3 Months Ended 9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Anti-dilutive securities (in shares) 20,473,931 6,594,117 15,172,265 7,741,317
Outstanding stock options        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Anti-dilutive securities (in shares) 1,643,506 808,855 1,643,506 817,855
Outstanding restricted stock units        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Anti-dilutive securities (in shares) 149,134 80,137 149,134 80,137
Warrants to purchase common stock associated with June 2016 Public Offering | Warrant        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Anti-dilutive securities (in shares) 0 421,867 0 421,867
March 2018 Public Offering Series 2 | Warrant        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Anti-dilutive securities (in shares) 798,810 798,810 798,810 798,810
December 2019 Public Offering | Warrant        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Anti-dilutive securities (in shares) 4,472,205 4,472,205 4,472,205 4,472,205
December 2020 Public Offering Series 1 | Warrant        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Anti-dilutive securities (in shares) 6,439,866 0 0 0
December 2020 Public Offering Series 2 | Warrant        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Anti-dilutive securities (in shares) 6,800,000 0 6,800,000 0
Warrants to purchase common stock associated with Loan Agreement | Warrant        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Anti-dilutive securities (in shares) 170,410 0 170,410 0
Warrants to purchase common stock associated with Solar loan agreement | Warrant        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Anti-dilutive securities (in shares) 0 12,243 0 12,243
Common stock associated with March 2019 Notes        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Anti-dilutive securities (in shares) 0 0 1,138,200 1,138,200