Quarterly report pursuant to Section 13 or 15(d)

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

v3.19.2
Equity Inventive Plans, Employee Stock Purchase Plan and Stock-Based Compensation - Additional Information (Details) - USD ($)
1 Months Ended 3 Months Ended 6 Months Ended 12 Months Ended
Sep. 26, 2018
Sep. 25, 2018
Feb. 28, 2017
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Dec. 31, 2018
Jan. 01, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Reserved common stock       7,540,249   7,540,249   6,250,381  
Aggregate intrinsic value of stock options exercised       $ 9,000 $ 75,000 $ 55,000 $ 135,000    
Weighted-average estimated grant-date fair value of employee stock options granted       $ 6.79   $ 6.97 $ 8.21    
Stock-based compensation expense       $ 2,463 232 $ 4,749 $ 481    
Restricted Stock Units                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Restricted common stock granted           154,900      
Shares vesting period           4 years      
Shares vesting date           2023-03      
Restricted Stock, Vested           0      
Stock-based compensation expense       600,000 0 $ 1,000,000 0    
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           2,717,022      
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       1,500   $ 1,500      
Remaining unrecognized compensation cost expected to be recognized over weighted-average period           2 years 4 months 24 days      
2018 Equity Incentive Plan | Employee Stock Options                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Stock-based compensation expense       1,900,000 200,000 $ 3,600,000 500,000    
Total unrecognized compensation cost related to unvested granted       21,400   $ 21,400      
Remaining unrecognized compensation cost expected to be recognized over weighted-average period           3 years 1 month 6 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       $ 0   $ 0      
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     389,571   389,571      
Shares available for grant 228,481                
Number of share purchase       68,910   68,910      
Stock-based compensation expense       $ 0 0 $ 100,000 0    
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       $ 17,000 16,000 $ 35,000 31,000    
Call options expiration period     1 year            
Share-based compensation arrangement by share-based payment award options, outstanding number of shares       105,000   105,000   210,000  
Share-based compensation arrangement by share-based payment award options, unvested shares       105,000   105,000   210,000  
Share-based compensation arrangement by share-based payment award options, shares granted           420,000      
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           210,000   210,000  
Other income (expense), net       $ 3,000 $ 4,000 $ 7,000 $ 4,000    
2017 Call Option Plan | SutroVax                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Reserved common stock       450,000   450,000      
2017 Call Option Plan | January 1 , 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                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Call options vesting percentage     25.00%            
2017 Call Option Plan | January 1 , 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                  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                  
Call options vesting percentage     25.00%