Quarterly report pursuant to Section 13 or 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 3 Months Ended 4 Months Ended 7 Months Ended 34 Months Ended 37 Months Ended
Sep. 26, 2018
Sep. 25, 2018
Aug. 31, 2019
Feb. 28, 2017
Mar. 31, 2020
Mar. 31, 2019
Dec. 31, 2019
Mar. 31, 2020
Dec. 31, 2019
Mar. 31, 2020
Jan. 01, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                      
Reserved common stock         8,693,572   7,357,234 8,693,572 7,357,234 8,693,572  
Aggregate intrinsic value of stock options exercised         $ 76,000 $ 46,000          
Weighted-average estimated grant-date fair value of employee stock options granted         $ 4.94 $ 5.86          
Stock-based compensation expense         $ 2,707,000 $ 2,286,000          
Restricted Stock Units                      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                      
Restricted common stock granted         478,000            
Shares vesting period         4 years            
Shares vesting date         2024-03            
Stock-based compensation expense         $ 600,000 500,000          
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                     1,154,948
Shares available for grant         2,144,785     2,144,785   2,144,785  
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         $ 6,900,000 $ 5,500,000   $ 6,900,000   $ 6,900,000  
Remaining unrecognized compensation cost expected to be recognized over weighted-average period         3 years 2 years 8 months 12 days          
2018 Equity Incentive Plan | Employee Stock Options                      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                      
Stock-based compensation expense         $ 1,900,000 $ 1,700,000          
Total unrecognized compensation cost related to unvested granted         $ 21,300,000 $ 22,500,000   21,300,000   21,300,000  
Remaining unrecognized compensation cost expected to be recognized over weighted-average period         2 years 9 months 18 days 3 years 4 months 24 days          
2018 Equity Incentive Plan | Employee Stock Purchase Plan                      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                      
Unrecognized stock-based compensation expense         $ 300,000 $ 0   $ 300,000   $ 300,000  
2018 Equity Incentive Plan | Maximum                      
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%                  
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       483,066     483,066   483,066  
Shares available for grant         206,404     206,404   206,404  
Shares available for grant, increase                     230,989
Stock-based compensation expense         $ 100,000 100,000          
2018 Employee Stock Purchase Plan | Maximum                      
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%                    
2017 Call Option Plan                      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                      
Stock-based compensation expense         138,000 18,000          
Other income (expense), net         $ 193,000 $ 4,000          
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                 315,000 420,000  
Exercise of common stock options, Shares                 315,000 315,000  
Share-based compensation arrangement by share-based payment award options, outstanding number of shares         105,000   105,000 105,000 105,000 105,000  
Share-based compensation arrangement by share-based payment award options, unvested shares             105,000   105,000    
2017 Call Option Plan | Option Granted in February 2017 | January 1 , 2017                      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                      
Call options vesting percentage       25.00%              
2017 Call Option Plan | Option Granted in February 2017 | January 1 , 2018                      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                      
Call options vesting percentage       25.00%              
2017 Call Option Plan | Option Granted in February 2017 | January 1 , 2019                      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                      
Call options vesting percentage       25.00%              
2017 Call Option Plan | Option Granted in February 2017 | January 1 , 2020                      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                      
Call options vesting percentage       25.00%              
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 15,000      
Exercise of common stock options, Shares             7,500 7,500      
Share-based compensation arrangement by share-based payment award options, outstanding number of shares         7,500   22,500 7,500 22,500 7,500  
Share-based compensation arrangement by share-based payment award options, unvested shares         15,000   22,500 15,000 22,500 15,000  
2017 Call Option Plan | Option Granted in August 2019 | January 1 , 2019                      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                      
Call options vesting percentage     25.00%                
2017 Call Option Plan | Option Granted in August 2019 | January 1 , 2020                      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                      
Call options vesting percentage     25.00%                
2017 Call Option Plan | Option Granted in August 2019 | January 1 , 2021                      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                      
Call options vesting percentage     25.00%                
2017 Call Option Plan | Option Granted in August 2019 | January 1 , 2022                      
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     450,000   450,000