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Stock-based Compensation - Narrative (Details) - USD ($)
1 Months Ended 6 Months Ended
Feb. 28, 2019
Jun. 30, 2019
Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting period   4 years  
Stock options granted (in shares)   1,348,290 242,458
Stock options forfeited (in shares)   74,903 124,909
Stock options exercised (in shares)   24,845 126,044
Unrecognized compensation costs   $ 18,212,000  
Unrecognized compensation cost, period of recognition   3 years 3 months 18 days  
Annual dividend yield   0.00% 0.00%
Restricted Stock      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Restricted stock granted (in shares)   0 0
Restricted stock forfeited (in shares)   0 0
Unrecognized compensation cost   $ 30,000  
Warrant      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Unrecognized compensation cost, period of recognition   1 year 6 months  
Unrecognized compensation cost   $ 944,000  
Warrants granted (in shares)   0 0
Warrants forfeited (in shares)   0 0
Employee stock purchase plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock purchase offering period   6 months  
Maximum stock purchase value per employee, percent of eligible compensation 15.00%    
Maximum stock purchase value per employee $ 25,000    
ESPP shares issued (in shares)   0 0
2018 Stock Option and Incentive Plan | Stock Option      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of shares authorized (in shares)   3,000,000  
Shares available for issusance as a percentage of outstanding shares, maximum   4.00%  
Term of options   10 years  
Number of shares available for issuance (in shares)   1,726,613  
Common Stock | Employee stock purchase plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Purchase price of common stock, percentage of fair market value 85.00%