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Stock Plans and Stock-Based Compensation - Performance-Based Restricted Stock Units - Additional Information (Details) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Stock-based compensation expense $ 3,541,000 $ 2,803,000 $ 20,257,000 $ 4,872,000
Performance-Based Restricted Stock Units        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Share-based compensation, number of stock unit grants in period     93,362  
Stock-based compensation expense $ 200,000 $ 0 $ 400,000 $ 0
Award achievement probability percentage 100.00%   100.00%  
Unrecognized compensation expense $ 4,800,000   $ 4,800,000  
Weighted-average amortization period     2 years 9 months  
Number of stock units vested     0  
Performance-Based Restricted Stock Units | Tranche One        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Share-based compensation, compounded annual growth measurement period     2 years  
Share-based compensation, vesting stock percentage     50.00%  
Performance-Based Restricted Stock Units | Tranche Two        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Share-based compensation, compounded annual growth measurement period     3 years  
Performance-Based Restricted Stock Units | Minimum        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Share-based compensation, thresholds percentage of revenue growth     20.00%  
Share price $ 43.86   $ 43.86  
Performance-Based Restricted Stock Units | Maximum        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Share-based compensation, thresholds percentage of revenue growth     40.00%  
Share price $ 58.75   $ 58.75