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Incentive Plans (Schedule of Changes in Stock Options Outstanding) (Details)
$ / shares in Units, $ in Millions
 9 Months Ended
Sep. 30, 2023
USD ($)
$ / shares
shares
Number of Shares  
Beginning balance (in shares) | shares 313,950
Granted (in shares) | shares 38,100
Exercised (in shares) | shares (54,450)
Ending balance (in shares) | shares 297,600
Exercisable (in shares) | shares 167,100
Weighted Average Exercise Price  
Beginning balance (in dollars per share) | $ / shares $ 112.06
Granted (in dollars per share) | $ / shares 263.48
Exercised (in dollars per share) | $ / shares 76.08
Ending balance (in dollars per share) | $ / shares 138.02
Exercisable (in dollars per share) | $ / shares $ 97.47
Weighted Average Remaining Contractual Term (Years)  
Outstanding, weighted average remaining contractual term (in years) 4 years 1 month 6 days
Exercisable, weighted average remaining contractual term (in years) 3 years 1 month 6 days
Aggregate Intrinsic Value (Millions of Dollars)  
Outstanding, aggregate intrinsic value | $ $ 60.6
Exercisable, aggregate intrinsic value | $ $ 40.8