Annual report pursuant to Section 13 and 15(d)

Organization and Principal Activities - Additional Information (Details)

v3.20.4
Organization and Principal Activities - Additional Information (Details)
 12 Months Ended
Dec. 11, 2020
USD ($)
$ / shares
shares
May 14, 2020
USD ($)
$ / shares
shares
Feb. 28, 2020
USD ($)
Dec. 31, 2020
USD ($)
Segment
shares
Dec. 31, 2019
USD ($)
Dec. 31, 2018
shares
Organization Consolidation And Presentation Of Financial Statements [Line Items]            
Date of incorporation       Apr. 21, 2003    
Headquartered in       South San Francisco    
Headquartered in state       CA    
Number of operating segments | Segment       1    
Net proceeds from issuance of common stock       $ 251,415,000 $ (327,000)  
Accumulated deficit       227,873,000 $ 195,745,000  
Unrestricted cash, cash equivalents and marketable securities       $ 326,500,000    
Substantial doubt about going concern, within one year       false    
Loan and Security Agreement | Oxford Finance LLC and Silicon Valley Bank | Term A Loan            
Organization Consolidation And Presentation Of Financial Statements [Line Items]            
Term loan maximum borrowing capacity     $ 25,000,000.0      
Borrowed amount     25,000,000.0      
Repayment of outstanding principal amount     $ 9,600,000      
Common Stock            
Organization Consolidation And Presentation Of Financial Statements [Line Items]            
Shares of common stock | shares       19,550,000   5,667,000
At-the-Market (“ATM")            
Organization Consolidation And Presentation Of Financial Statements [Line Items]            
Gross proceeds from issuance of common stock       $ 24,600,000    
Underwriting discounts and commissions and other offering expenses       800,000    
Net proceeds from issuance of common stock       $ 23,800,000    
At-the-Market (“ATM") | Common Stock            
Organization Consolidation And Presentation Of Financial Statements [Line Items]            
Shares of common stock | shares       2,614,286    
Public Offering            
Organization Consolidation And Presentation Of Financial Statements [Line Items]            
Gross proceeds from issuance of common stock $ 144,900,000 $ 98,000,000.0        
Underwriting discounts and commissions and other offering expenses 9,100,000 6,600,000        
Net proceeds from issuance of common stock $ 135,800,000 $ 91,400,000        
Public Offering | Common Stock            
Organization Consolidation And Presentation Of Financial Statements [Line Items]            
Shares of common stock | shares 6,900,000 12,650,000        
Public offering price per share | $ / shares $ 21.00 $ 7.75        
Underwriters’ Option to Purchase Shares | Common Stock            
Organization Consolidation And Presentation Of Financial Statements [Line Items]            
Shares of common stock | shares 900,000 1,650,000        
Minimum            
Organization Consolidation And Presentation Of Financial Statements [Line Items]            
Period from issuance date of unaudited interim condensed financial statements       12 months