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Share-based Compensation - Performance Units Rollforward (Details) - Performance units - $ / shares
shares in Thousands
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Number of Shares      
Unvested at beginning of year (shares) 70    
Granted (shares) 30    
Vested (shares) (10)    
Forfeited (shares) 0    
Unvested at end of year (shares) 90 70  
Weighted-Average Grant-Date Fair Value      
Unvested at beginning or year (usd per share) $ 66.76    
Granted (usd per share) 118.41 $ 67.50 $ 69.53
Vested (usd per share) 51.68    
Forfeited (usd per share) 118.41    
Unvested at end or year (usd per share) $ 84.44 $ 66.76