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Stock-Based Compensation - 2018 Employee Stock Purchase Plan (Details) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Jan. 01, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Proceeds from stock issued in connection with the employee stock purchase plan $ 15,129 $ 0 $ 0  
Employee stock purchase plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Common stock reserved for issuance (in shares)       1,396,896
Shares available for grant (in shares) 4,620,087      
Percentage of employee earnings allowed 15.00%      
Discount price percentage 85.00%      
Offering period (up to) 27 months      
Employee contributions $ 5,400      
Common stock purchased (in shares) 776,809      
Weighted-average purchase price per share (in USD per share) $ 19.48      
Unrecognized stock-based compensation expense $ 8,500      
Remaining offering period 1 year 8 months 12 days