Quarterly report pursuant to Section 13 or 15(d)

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

v3.20.2
Stockholder's Equity - Schedule of Reserved Shares of Common Stock for Future Issuance (Detail) - shares
Sep. 30, 2020
Dec. 31, 2019
Class of Stock [Line Items]    
Common shares reserved for future issuance 9,545,176 8,143,816
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 1,622,138 0
2014 Equity Incentive Plan    
Class of Stock [Line Items]    
Common shares reserved for future issuance 161,776 55,478
2014 Employee Stock Purchase Plan    
Class of Stock [Line Items]    
Common shares reserved for future issuance 5,895 7,423
2015 Inducement Award Plan    
Class of Stock [Line Items]    
Common shares reserved for future issuance 14,050 31,550
June 2016 Public Offering | Warrant liability    
Class of Stock [Line Items]    
Common shares reserved for future issuance 421,867 421,867
March 2018 Public Offering | Series 1 Warrant    
Class of Stock [Line Items]    
Common shares reserved for future issuance 798,810 798,810
December 2019 Public Offering | Warrant liability    
Class of Stock [Line Items]    
Common shares reserved for future issuance 4,472,205 4,472,205
December 2019 Public Offering | Option to Purchase Common Stock    
Class of Stock [Line Items]    
Common shares reserved for future issuance 0 583,333
Warrants to purchase common stock associated with Solar loan agreement | Warrant liability    
Class of Stock [Line Items]    
Common shares reserved for future issuance 12,243 12,243
Stock options    
Class of Stock [Line Items]    
Common shares reserved for future issuance 817,855 526,070
Restricted Stock Units    
Class of Stock [Line Items]    
Common shares reserved for future issuance 80,137 96,637