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Stock Incentive Plans - Summary of Non-vested Restricted Stock Units ("RSUs") (Details) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Shares Underlying RSUs      
Options Granted (in shares) 0    
RSUs issued and unvested      
Shares Underlying RSUs      
Beginning balance (in shares) 886,030 547,891  
Options Granted (in shares) 595,915 629,901  
Vested (in shares) (235,915) (180,842)  
Forfeited (in shares) (131,871) (110,920)  
Ending balance (in shares) 1,114,159 886,030 547,891
Weighted Average Grant Date Fair Value      
Beginning balance (in USD per share) $ 77.92 $ 56.62  
Granted (in USD per share) 104.09 87.72  
Vested (in USD per share) 69.01 52.52  
Forfeited (in USD per share) 59.85 69.77  
Ending balance (in USD per share) $ 94.25 $ 77.92 $ 56.62
Weighted Remaining Vesting Period (in years)      
Weighted remaining vesting period of RSUs (in years) 1 year 4 months 17 days 1 year 4 months 20 days 2 years 5 months 12 days
Aggregate Intrinsic Value (in thousands)      
Aggregate intrinsic value of RSUs $ 264,290 $ 60,330 $ 38,067