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Stock-Based Compensation - Stock Options (Details) - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting period (in years) 5 years    
Repurchase of unvested shares (in shares) 147,153 0 0
Granted (in shares) 143,650 186,500 219,450
Weighted average grant date fair value for stock options (USD per share) $ 16.79 $ 25.01 $ 19.43
Fair value of stock options vested during period $ 3,600,000 $ 3,400,000 $ 3,500,000
Aggregate intrinsic value of stock options exercised during period 33,423,000 15,100,000 32,700,000
Compensation cost not yet recognized on nonvested awards 4,100,000    
Cash received from exercise of stock options $ 10,200,000 $ 2,500,000 $ 5,200,000
Stock options and assumed options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Dividend rate (percent) 0.00% 0.00% 0.00%
Compensation cost not yet recognized, period for recognition (in years) 2 years 6 months    
2009 and 2015 Plan | Accounts Payable, Accrued Expenses and Other Current Liabilities      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Liability from proceeds of early exercise of stock options $ 0 $ 100,000  
2009 and 2015 Plan | Stock options and assumed options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting period (in years) 5 years    
Award expiration period (in years) 10 years    
Common Stock | 2009 and 2015 Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Unvested shares of common stock outstanding (shares) 0 250  
Common Stock | 2009 and 2015 Plan | Stock options and assumed options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Repurchase of unvested shares (in shares) 0 27