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Share-Based Compensation - Restricted shares based on performance conditions (Details) - USD ($)
$ / shares in Units, $ in Millions
1 Months Ended 12 Months Ended
Jan. 31, 2020
Dec. 31, 2022
Dec. 31, 2021
Dec. 31, 2020
Performance based restricted shares        
Share-Based Compensation        
Shares awarded during period 59,490      
Vesting period 3 years      
Aggregate fair value at grant date $ 8.8      
Restricted shares outstanding        
Outstanding at the beginning of the period (in shares))   56,000    
Granted (in shares) 59,490      
Vested (in shares)   (36,000)    
Outstanding at the end of the period (in shares)   20,000 56,000  
Weighted-Average Grant-Date Fair Value        
Outstanding at the beginning of the period (in dollars per share)   $ 150.02    
Vested (in dollars per share)     $ 151.13  
Outstanding at the end of the period (in dollars per share)   $ 148.00 $ 150.02  
Performance based restricted stock units        
Share-Based Compensation        
Shares awarded during period   49,065 95,902 31,204
Vesting period   3 years    
Restricted shares outstanding        
Outstanding at the beginning of the period (in shares))   107,000    
Granted (in shares)   49,065 95,902 31,204
Vested (in shares)   (43,000)    
Outstanding at the end of the period (in shares)   113,000 107,000  
Weighted-Average Grant-Date Fair Value        
Outstanding at the beginning of the period (in dollars per share)   $ 94.26    
Granted (in dollars per share)   81.09    
Vested (in dollars per share)   102.94    
Outstanding at the end of the period (in dollars per share)   $ 85.31 $ 94.26  
Performance based restricted stock units | Minimum        
Weighted-Average Grant-Date Fair Value        
Vesting percentage   30.00%    
Performance based restricted stock units | Maximum        
Weighted-Average Grant-Date Fair Value        
Vesting percentage   200.00%