Quarterly report pursuant to Section 13 or 15(d)

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

v3.19.1
Equity Inventive Plans, Employee Stock Purchase Plan and Stock-Based Compensation - Additional Information (Details) - USD ($)
1 Months Ended 3 Months Ended 12 Months Ended
Sep. 26, 2018
Feb. 28, 2017
Mar. 31, 2019
Mar. 31, 2018
Dec. 31, 2018
Dec. 31, 2017
Sep. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]              
Reserved common stock     7,543,257   6,250,381    
Aggregate intrinsic value of stock options exercised     $ 46,116 $ 60,000      
Weighted-average estimated grant-date fair value of employee stock options granted     $ 5.86 $ 8.39      
Total fair value of stock options vested     $ 1,700,000 $ 200,000      
Stock-based compensation expense     $ 2,286 249      
Share-based compensation arrangement by share-based payment award options vested number of shares         210,000    
Share-based compensation arrangement by share-based payment award options exercised shares         210,000    
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     $ 500,000 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 2,742,059            
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     $ 5,500        
Remaining unrecognized compensation cost expected to be recognized over weighted-average period     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     $ 1,700,000 200,000      
Total unrecognized compensation cost related to unvested granted     $ 22,500        
Remaining unrecognized compensation cost expected to be recognized over weighted-average period     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     $ 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        
Shares available for grant 228,481            
Number of share purchase     68,910        
Stock-based compensation expense     $ 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     $ 18,000 15,000      
Call options expiration period   1 year          
Share-based compensation arrangement by share-based payment award options, outstanding number of shares             315,000
Share-based compensation arrangement by share-based payment award options, unvested shares             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        
Share-based compensation arrangement by share-based payment award options exercised shares     210,000        
Other income (expense), net     $ 4,000 $ 0      
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%