Annual report pursuant to Section 13 and 15(d)

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

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Stockholders' Equity (Deficit) - Schedule of Common Stock Reserved for Future Issuance (Details) - shares
Dec. 31, 2018
Dec. 31, 2017
Temporary Equity [Line Items]    
Reserved common stock 6,250,381 6,084,499
Redeemable Convertible Preferred Stock    
Temporary Equity [Line Items]    
Reserved common stock   5,063,404
Common Stock    
Temporary Equity [Line Items]    
Reserved common stock 3,111,718 835,320
Common Stock Award Issued And Outstanding    
Temporary Equity [Line Items]    
Reserved common stock 311,240  
2004 and 2018 Equity Incentive Plan    
Temporary Equity [Line Items]    
Reserved common stock 2,525,610 91,149
2018 Employee Stock Purchase Plan    
Temporary Equity [Line Items]    
Reserved common stock 230,000  
Warrants To Purchase Redeemable Convertible    
Temporary Equity [Line Items]    
Reserved common stock   93,527
Warrant to Purchase Common Stock    
Temporary Equity [Line Items]    
Reserved common stock 71,813 1,099