Annual report pursuant to Section 13 and 15(d)

Equity Incentive Plans, Employee Stock Purchase Plan and Stock-Based Compensation - Additional Information (Details)

v3.20.1
Equity Incentive Plans, Employee Stock Purchase Plan and Stock-Based Compensation - Additional Information (Details) - USD ($)
1 Months Ended 12 Months Ended
Sep. 26, 2018
Sep. 25, 2018
Aug. 31, 2019
Feb. 28, 2017
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Jan. 01, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Reserved common stock         7,357,234 6,250,381    
Aggregate intrinsic value of stock options exercised         $ 200,000 $ 200,000 $ 100,000  
Weighted-average estimated grant-date fair value of employee stock options granted         $ 6.71 $ 9.48 $ 7.26  
Total fair value of stock options vested         $ 1,100,000 $ 2,300,000 $ 1,600,000  
Stock-based compensation expense         $ 10,312,000 $ 2,872,000 1,391,000  
Restricted Stock Units                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Restricted common stock granted         154,900 312,400    
Shares vesting period         4 years      
Shares vesting date         2023-03      
Stock-based compensation expense         $ 2,100,000 $ 400,000    
2018 Equity Incentive Plan                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Reserved common stock   2,300,000            
Annual increase period of common stock reserved for issuance   10 years            
Maximum number of shares issuable               1,142,409
Shares available for grant         2,750,416      
2018 Equity Incentive Plan | Restricted Stock Units                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Total unrecognized compensation cost related to unvested granted         $ 3,700,000 $ 3,900,000    
Remaining unrecognized compensation cost expected to be recognized over weighted-average period         2 years 2 years    
2018 Equity Incentive Plan | Employee Stock Options                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Stock-based compensation expense         $ 7,700,000 $ 2,400,000    
Total unrecognized compensation cost related to unvested granted         $ 16,900,000 $ 18,200,000    
Remaining unrecognized compensation cost expected to be recognized over weighted-average period         2 years 8 months 12 days 3 years 6 months    
2018 Equity Incentive Plan | Employee Stock Purchase Plan                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Unrecognized stock-based compensation expense         $ 100,000 $ 100,000    
2018 Employee Stock Purchase Plan                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Reserved common stock 230,000              
Annual increase period of common stock reserved for issuance 10 years              
Maximum number of shares issuable 2,300,000       326,542      
Shares available for grant         131,939      
Shares available for grant, increase               228,481
Stock-based compensation expense         $ 500,000 100,000    
2017 Call Option Plan                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Stock-based compensation expense         78,000 65,000 79,000  
Other income (expense), net         $ 153,000 $ 133,000 $ 109,000  
2017 Call Option Plan | Option Granted in February 2017                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Share-based compensation arrangement by share-based payment award options, shares granted       420,000 420,000      
Call options expiration period       1 year        
Share-based compensation arrangement by share based payment award options, exercise price per share         $ 0.76      
Share-based compensation arrangement by share-based payment award options vested number of shares         315,000 210,000    
Share-based compensation arrangement by share-based payment award options exercised shares         315,000 210,000    
Share-based compensation arrangement by share-based payment award options, outstanding number of shares         105,000 210,000    
Share-based compensation arrangement by share-based payment award options, unvested shares         105,000 210,000    
2017 Call Option Plan | Option Granted in August 2019                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Share-based compensation arrangement by share-based payment award options, shares granted     30,000   30,000      
Call options expiration period     1 year          
Share-based compensation arrangement by share based payment award options, exercise price per share         $ 1.21      
Share-based compensation arrangement by share-based payment award options vested number of shares         7,500      
Share-based compensation arrangement by share-based payment award options exercised shares         7,500      
Share-based compensation arrangement by share-based payment award options, outstanding number of shares         22,500      
Share-based compensation arrangement by share-based payment award options, unvested shares         22,500      
2017 Call Option Plan | January 1 , 2017 | Option Granted in February 2017                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Call options vesting percentage       25.00%        
2017 Call Option Plan | January 1 , 2018 | Option Granted in February 2017                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Call options vesting percentage       25.00%        
2017 Call Option Plan | January 1 , 2019 | Option Granted in February 2017                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Call options vesting percentage       25.00%        
2017 Call Option Plan | January 1 , 2019 | Option Granted in August 2019                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Call options vesting percentage     25.00%          
2017 Call Option Plan | January 1 , 2020 | Option Granted in February 2017                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Call options vesting percentage       25.00%        
2017 Call Option Plan | January 1 , 2020 | Option Granted in August 2019                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Call options vesting percentage     25.00%          
2017 Call Option Plan | January 1 , 2021 | Option Granted in August 2019                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Call options vesting percentage     25.00%          
2017 Call Option Plan | January 1 , 2022 | Option Granted in August 2019                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Call options vesting percentage     25.00%          
2017 Call Option Plan | SutroVax                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Reserved common stock         450,000      
Maximum [Member] | 2018 Equity Incentive Plan                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Increase in stock reserved for issuance as percentage of capital stock outstanding on last day of preceding year   5.00%            
Maximum [Member] | 2018 Employee Stock Purchase Plan                
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                
Increase in stock reserved for issuance as percentage of capital stock outstanding on last day of preceding year 1.00%