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Stock-Based Compensation - Summary of 2009 ESPP (Details) - $ / shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted average per share discount from market value for shares purchased (in dollars per share) $ 22.97 $ 17.83 $ 13.10
The 2009 ESPP      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares purchased pursuant to 2009 ESPP 113,778    
Weighted average per share price of shares purchased (in dollars per share) $ 130.17    
Weighted average per share discount from market value for shares purchased (in dollars per share) $ 22.97    
Shares available for purchase pursuant to 2009 ESPP 1,412,727