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Stock Compensation Plans (Narrative) (Details) - USD ($)
$ in Millions
1 Months Ended 12 Months Ended
Jan. 30, 2024
Apr. 27, 2023
Feb. 27, 2024
Jan. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Common stock, shares issuable (in shares)         150,000,000 150,000,000  
Stock compensation expense         $ 46.4 $ 34.0 $ 27.6
Tax benefit from share-based compensation arrangements         $ 0.5 $ 1.9 3.3
Performance Shares              
Shares granted (in shares)         289,742    
Shares earned (in share)         210,269    
Compensation cost related to unearned performance awards         $ 39.3    
Recognition period         1 year 6 months    
Number of shares not vested (in shares)         571,382 543,904  
Performance Shares | Subsequent event              
Shares granted (in shares) 170,735            
Shares issued (in shares)     133,569        
Shares withheld for taxes (in shares)     76,700        
Performance Shares | Certain retirees and other individuals              
Shares earned (in share)           9,080  
Restricted Stock Units (RSUs)              
Service period         3 years    
Shares granted (in shares)         117,840    
Compensation cost related to unearned performance awards         $ 15.7    
Recognition period         1 year 6 months    
Award vesting rights, share conversion ratio         1    
Number of shares not vested (in shares)         213,947 213,198  
Restricted Stock Units (RSUs) | Tranche one              
Award vesting percentage         33.33%    
Restricted Stock Units (RSUs) | Tranche two              
Award vesting percentage         33.33%    
Restricted Stock Units (RSUs) | Tranche three              
Award vesting percentage         33.33%    
Restricted Stock Units (RSUs) | Subsequent event              
Shares granted (in shares) 123,520            
RSUs issued after shares withheld for taxes (in shares)       51,239      
Shares withheld for taxes (in shares)       31,390      
Stock Appreciation Rights (SSARs)              
Stock compensation expense         $ 0.2 $ 0.5 $ 0.8
Total fair value of awards vested         $ 0.4    
Awards outstanding (in shares)         56,350    
Number of shares not vested (in shares)         16,900    
Total intrinsic value of outstanding awards         $ 2.9    
Total intrinsic value of exercisable of awards         2.1    
Total intrinsic value of awards exercised         4.9    
Restricted Stock              
RSUs issued after shares withheld for taxes (in shares)   10,524          
Stock compensation expense         $ 1.5    
Weighted-average period for compensation cost expected to be recognized         1 year    
Restricted common stocks issued (in shares)   12,069          
2006 Long-Term Incentive Plan              
Common stock, shares issuable (in shares)         10,000,000    
Shares available for grant (in shares)         3,650,232    
Long Term Incentive Plan              
Service period         3 years    
Long Term Incentive Plan | Minimum              
Target award percentages         16.50%    
Long Term Incentive Plan | Maximum              
Target award percentages         200.00%