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Stock compensation plans (Tables)
 12 Months Ended
Dec. 31, 2023
Share-Based Payment Arrangement, Noncash Expense [Abstract]  
Summary of Share-based Compensation Activity The following table summarizes the share-based compensation activity:
202320222021
Share-based compensation expense$31,465 $27,224 $22,937 
Total income tax benefit recognized for share-based compensation arrangements7,820 6,824 10,912 
Net excess tax benefit1,351 1,292 6,355 
Weighted-Average Assumptions used to Estimate Fair Value of Options Granted
The fair value of options granted in 2023, 2022 and 2021 was estimated at the date of grant using a Black-Scholes option pricing model. The following weighted-average assumptions were used:
 202320222021
Risk-free interest rate4.13 %1.56 %0.67 %
Expected life of option5.07 years5.03 years5.01 years
Expected dividend yield0.57 %0.41 %0.34 %
Expected volatility31.42 %30.09 %30.03 %
Summary of Stock Option Activity
The following table summarizes the option activity during 2023:
Shares Subject to OptionsWeighted Average Exercise PriceWeighted Average Remaining Contractual Life In Years
Aggregate
Intrinsic
Value
Outstanding, beginning of the year1,228,848 $230.58 
Granted189,388 238.92 
Exercised(99,799)108.19 
Forfeited or expired(24,662)319.20 
Outstanding, end of the year1,293,775 239.55 4.7$55,105 
Exercisable, end of the year988,794 $226.34 3.5$52,939 
Weighted-Average Assumptions used to Estimate Fair Value of Non-Vested Shares Granted The following weighted-average assumptions were used:
202320222021
Risk-free interest rate4.53 %1.57 %0.28 %
Expected dividend yield0.57 %0.42 %0.34 %
Summary of Non-Vested Restricted Stock Unit Activity
The following table summarizes the non-vested restricted stock unit activity during 2023:
Number of
Non-Vested
Shares
Weighted
Average
Grant-Date
Fair Value
Weighted
Average
Remaining
Contractual
Life
Aggregate
Intrinsic
Value
Outstanding, beginning of the year147,968 $349.42 
Granted98,201 235.14 
Vested(34,623)346.01 
Forfeited(21,046)318.02 
Outstanding, end of the year190,500 $294.63 1.4$47,709