Annual report pursuant to Section 13 and 15(d)

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

v3.19.1
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
Sep. 30, 2018
Feb. 28, 2017
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Reserved common stock         6,250,381 6,084,499  
Aggregate intrinsic value of stock options exercised         $ 200,000 $ 100,000 $ 300,000
Weighted-average estimated grant-date fair value of employee stock options granted         $ 9.48 $ 7.26 $ 7.62
Total fair value of stock options vested         $ 2,300,000 $ 1,600,000 $ 900,000
Stock-based compensation expense         2,872,000 1,391,000 968,000
Other income (expense), net         $ 1,913,000 (77,000) $ 87,000
Restricted Stock Units              
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Restricted common stock granted     312,400   312,400    
Fair values of the common stock price per share     3 years        
Shares vesting date     2021-09        
Restricted Stock, Vested         0    
Stock-based compensation expense         $ 400,000    
2018 Equity Incentive Plan              
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Reserved common stock   2,300,000          
Increase in stock reserved for issuance as percentage of capital stock outstanding on last day of preceding year   5.00%          
Shares available for grant         2,525,610    
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         $ 3,900,000    
Remaining unrecognized compensation cost expected to be recognized over weighted-average period         2 years 6 months    
2018 Equity Incentive Plan | Stock Options              
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Stock-based compensation expense         $ 2,400,000    
Total unrecognized compensation cost related to unvested granted         $ 18,200,000    
Remaining unrecognized compensation cost expected to be recognized over weighted-average period         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    
ESPP              
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       230,000    
Stock-based compensation expense         $ 100,000    
2017 Call Option Plan              
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Stock-based compensation expense         $ 65,000 $ 79,000  
Call options expiration period       1 year      
Share-based compensation arrangement by share-based payment award options, outstanding number of shares         210,000 315,000  
Share-based compensation arrangement by share-based payment award options, unvested shares         210,000 315,000  
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 exercised number of shares         210,000 105,000  
Share-based compensation arrangement by share-based payment award options vested number of shares         210,000 105,000  
Other income (expense), net         $ 133,000 $ 109,000  
2017 Call Option Plan | SutroVax              
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Reserved common stock         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%      
Maximum | 2018 Equity Incentive Plan              
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Annual increase period of common stock reserved for issuance   10 years          
Maximum | ESPP              
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%