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Stock Plans and Stock-Based Compensation - Employee Stock Purchase Plan - Additional Information (Details) - USD ($)
$ in Thousands
12 Months Ended
Sep. 15, 2017
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Sep. 15, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Shares reserved for issuance   3,554,612      
Total recognized compensation cost   $ 25,825 $ 9,299 $ 3,101  
2016 Employee Stock Purchase Plan          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Shares reserved for issuance         500,000
Purchase price as percentage of fair market value of common stock 85.00%        
Shares purchased under the plan   74,517 128,786    
Total recognized compensation cost   $ 700 $ 600    
Cost amortized weighted-average period   3 months      
Unrecognized compensation cost   $ 200      
Maximum | 2016 Employee Stock Purchase Plan          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Increase in number of shares reserved and available for issuance         200,000
Common Stock | 2016 Employee Stock Purchase Plan          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Increase in number of shares reserved and available for issuance, percentage 1.00%        
Common Stock | Maximum | 2016 Employee Stock Purchase Plan          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Purchase price, discount percentage 15.00%