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Stock-Based Compensation - Narrative (Details)
$ in Thousands
4 Months Ended 8 Months Ended 12 Months Ended
Jan. 01, 2021
shares
Jan. 01, 2020
shares
Jan. 01, 2019
shares
Apr. 30, 2020
Dec. 31, 2020
USD ($)
purchase_period
shares
Dec. 31, 2020
USD ($)
shares
Dec. 31, 2019
USD ($)
shares
Oct. 31, 2018
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Aggregate intrinsic value of options exercised | $           $ 5,600 $ 6,800  
Unrecognized compensation costs | $         $ 3,200 $ 3,200    
Early exercise of stock options, share subject to repurchase (in shares) | shares         5,836 5,836 21,404  
Issuance of common stock related to employee stock purchase plan (in shares) | shares           137,377 168,457  
Issuance of common stock related to employee stock purchase plan | $           $ 1,915 $ 2,203  
Stock-based compensation expense | $           $ 11,927 7,464  
Minimum                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Exercise price of option as percent of fair market value when individual owns more than 10% of shares outstanding (percent)           110.00%    
Stock Options                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Percentage of ownership of outstanding shares for alternate terms           10.00%    
Stock option term (in years)           10 years    
Stock option term when grantee holds more than 10% of shares outstanding (in years)           5 years    
Award vesting period (in years)           4 years    
Unrecognized compensation cost, expected period for recognition (in years)           1 year 10 months 24 days    
Incentive Stock Options | Minimum                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Exercise price of option as percent of fair market value (percent)           100.00%    
Nonqualified Stock Options | Minimum                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Exercise price of option as percent of fair market value (percent)           85.00%    
Restricted Stock Units                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Unrecognized compensation cost, expected period for recognition (in years)           2 years 10 months 24 days    
Unrecognized compensation cost | $         $ 19,300 $ 19,300    
Restricted Stock Units | Minimum                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Award vesting period (in years)           2 years    
Restricted Stock Units | Maximum                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Award vesting period (in years)           4 years    
2018 Equity Incentive Plan                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Annual increase in shares reserved as percentage of prior year-end shares outstanding (percent)         5.00% 5.00%    
Increase in number of shares reserved for future issuance (in shares) | shares   1,222,538 1,258,190          
Shares available for future grants (in shares) | shares         2,843,814 2,843,814    
2018 Equity Incentive Plan | Subsequent Event                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Increase in number of shares reserved for future issuance (in shares) | shares 1,629,161              
2018 ESPP                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Annual increase in shares reserved as percentage of prior year-end shares outstanding (percent)         1.00% 1.00%    
Annual increase in shares reserved, maximum (in shares) | shares         555,555 555,555    
Unrecognized compensation cost | $         $ 200 $ 200    
Purchase price of common stock as a percent of fair market value (percent)           85.00%    
Employees stock purchase program offering period interval (in months)       6 months 12 months      
Number of purchase periods in offering interval | purchase_period         2      
Number of shares reserved for issuance (in shares) | shares         705,618 705,618   515,307
Accrued compensation and related expenses for employee payroll deductions | $         $ 400 $ 400 200  
Stock-based compensation expense | $           $ 1,200 $ 800  
2018 ESPP | Subsequent Event                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Increase in number of shares reserved for future issuance (in shares) | shares 325,832