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Share-Based Compensation - Information for Restricted Stock Units under Equity Incentive Plan (Details) - $ / shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Weighted Average Grant Date Fair Value      
Granted (usd per share) $ 199.51 $ 243.65 $ 294.50
Closing stock price $ 387.83    
Restricted stock units      
Shares      
Nonvested, beginning of period (in shares) 847,972    
Granted (in shares) 460,671    
Vested (in shares) (261,302)    
Forfeited (in shares) (52,292)    
Nonvested, end of period (in shares) 995,049 847,972  
Weighted Average Grant Date Fair Value      
Nonvested, beginning of period (usd per share) $ 236.54    
Granted (usd per share) 199.51    
Vested (usd per share) 209.30    
Forfeited (usd per share) 225.66    
Nonvested, end of period (usd per share) $ 227.12 $ 236.54