Quarterly report pursuant to Section 13 or 15(d)

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

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Stockholders' Equity - Schedule of Common Stock Reserved for Future Issuance (Details) - shares
Mar. 31, 2020
Dec. 31, 2019
Temporary Equity [Line Items]    
Reserved common stock 8,693,572 7,357,234
Common Stock    
Temporary Equity [Line Items]    
Reserved common stock 5,145,635 3,872,664
Common Stock Awards Issued And Outstanding    
Temporary Equity [Line Items]    
Reserved common stock 767,016 335,799
2004 and 2018 Equity Incentive Plan    
Temporary Equity [Line Items]    
Reserved common stock 2,144,785 2,750,416
2018 Employee Stock Purchase Plan    
Temporary Equity [Line Items]    
Reserved common stock 483,066 326,542
Warrants to Purchase Common Stock    
Temporary Equity [Line Items]    
Reserved common stock 153,070 71,813