Quarterly report pursuant to Section 13 or 15(d)

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

v3.19.3
Equity Incentive Plans, Employee Stock Purchase Plan and Stock-Based Compensation - Additional Information (Details) - USD ($)
1 Months Ended 3 Months Ended 9 Months Ended 12 Months Ended
Sep. 26, 2018
Sep. 25, 2018
Aug. 31, 2019
Feb. 28, 2017
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Dec. 31, 2018
Jan. 01, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]                    
Reserved common stock         7,367,236   7,367,236   6,250,381  
Aggregate intrinsic value of stock options exercised         $ 63,000 $ 18,000 $ 119,000 $ 153,000    
Weighted-average estimated grant-date fair value of employee stock options granted         $ 4.88 $ 8.93 $ 6.74 $ 8.93    
Stock-based compensation expense         $ 2,880 $ 321 $ 7,629 $ 802    
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      
Stock-based compensation expense         $ 600,000 0 $ 1,600,000 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         2,650,411   2,650,411      
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         $ 4,300,000   $ 4,300,000      
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         2,000,000 300,000 $ 5,600,000 800,000    
Total unrecognized compensation cost related to unvested granted         20,000,000   $ 20,000,000      
Remaining unrecognized compensation cost expected to be recognized over weighted-average period             2 years 10 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   $ 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       326,542   326,542      
Shares available for grant         131,939   131,939      
Shares available for grant, increase                   228,481
Stock-based compensation expense         $ 300,000 0 $ 400,000 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         24,000 19,000 59,000 50,000    
Other income (expense), net         $ (15,000) $ 6,000 $ (8,000) $ 10,000    
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             210,000   210,000  
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  
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             0      
Share-based compensation arrangement by share-based payment award options, outstanding number of shares         22,500   22,500      
Share-based compensation arrangement by share-based payment award options, unvested shares         22,500   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   450,000