Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity - Schedule of Reserved Shares of Common Stock for Future Issuance (Detail)

v3.21.2
Stockholders' Equity - Schedule of Reserved Shares of Common Stock for Future Issuance (Detail) - shares
Jun. 30, 2021
Dec. 31, 2020
Class of Stock [Line Items]    
Common shares reserved for future issuance 25,249,113 28,028,978
Stock options    
Class of Stock [Line Items]    
Common shares reserved for future issuance 1,607,080 830,343
Restricted Stock Units    
Class of Stock [Line Items]    
Common shares reserved for future issuance 134,774 29,087
Warrant | June 2016 Public Offering    
Class of Stock [Line Items]    
Common shares reserved for future issuance 0 421,867
Warrant | December 2019 Public Offering    
Class of Stock [Line Items]    
Common shares reserved for future issuance 4,472,205 4,472,205
Warrant | December 2020 Public Offering Series 1    
Class of Stock [Line Items]    
Common shares reserved for future issuance 6,439,866 6,800,000
Warrant | December 2020 Public Offering Series 2    
Class of Stock [Line Items]    
Common shares reserved for future issuance 6,800,000 6,800,000
Warrant | Prefunded Warrants to Purchase Common Stock Associated with December 2020 Public Offering    
Class of Stock [Line Items]    
Common shares reserved for future issuance 3,200,000 5,260,000
Warrant | Warrants to purchase common stock associated with Solar loan agreement    
Class of Stock [Line Items]    
Common shares reserved for future issuance 12,243 12,243
Warrant | Warrants to purchase common stock associated with Loan Agreement    
Class of Stock [Line Items]    
Common shares reserved for future issuance 170,410 0
Series 1 Warrant | March 2018 Public Offering    
Class of Stock [Line Items]    
Common shares reserved for future issuance 798,810 798,810
March 2019 Notes    
Class of Stock [Line Items]    
Common shares reserved for future issuance 1,138,200 1,138,200
April 2020 Notes    
Class of Stock [Line Items]    
Common shares reserved for future issuance 0 1,299,790
2014 Employee Stock Purchase Plan    
Class of Stock [Line Items]    
Common shares reserved for future issuance 6,652 5,895
2014 Plan    
Class of Stock [Line Items]    
Common shares reserved for future issuance 217,923 146,488
2015 Plan    
Class of Stock [Line Items]    
Common shares reserved for future issuance 250,950 14,050