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Share-Based Compensation (Tables)
 12 Months Ended
Dec. 31, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Stock Option Activity
The following table summarizes stock option activity under our share-based plans for the year ended December 31, 2023:
 SharesWeighted Average
Exercise Price		Weighted Average
Remaining
Contractual Term
(Years)		Aggregate
Intrinsic Value
Balance at December 31, 2022642,925 $154.57   
Granted33,408 357.52   
Less: Exercised
90,439 92.52   
           Forfeited15,172 293.44   
Balance at December 31, 2023570,722 $173.13 4.22$129,309,839 
Exercisable at December 31, 2023371,551 $102.10 2.48$110,210,899 
Stock options outstanding and exercisable by exercise price range
The following table presents information about stock options outstanding and exercisable at December 31, 2023:
 Outstanding
Stock Options		Exercisable
Stock Options
Range of Exercise PricesSharesWeighted Average
Remaining
Contractual Term
(Years)		Weighted Average Exercise PriceSharesWeighted Average Exercise Price
$58.26 to $80.78
214,410 1.26$70.78 214,410 $70.78 
$80.79 to $220.01
216,574 4.53155.78 155,415 142.35 
$220.02 to $515.41
139,738 8.26357.05 1,726 370.02 
 570,722 4.22$173.13 371,551 $102.10 
Summary of cash proceeds and tax benefits realized from stock option exercise.
The following table summarizes the cash proceeds and tax benefits realized from the exercise of stock options:
 Year Ended December 31,
(in thousands, except share amounts)202320222021
Options exercised90,439 71,737 274,253 
Cash proceeds$8,368 $6,247 $14,435 
Intrinsic value of options exercised$23,356 $21,976 $118,305 
Tax benefits realized$5,839 $5,494 $29,576 
Summary of assumptions for estimated fair value of employee stock option awards at grant date
We estimated the fair value of employee stock option awards at the grant date based on the assumptions summarized in the following table:
 
 Year Ended December 31,
(Weighted average)202320222021
Expected volatility31.0 %28.9 %27.0 %
Expected term7.4years7.1years6.9years
Risk-free interest rate4.01 %2.92 %1.00 %
Expected dividend yield1.15 %1.15 %1.15 %
Grant date fair value$130.74  $116.56  $83.05  
Summary of restricted share activity
The table below presents restricted stock award activity under our share-based plans for the year ended December 31, 2023:
 SharesWeighted Average
Grant Date Fair Value
Balance unvested at December 31, 2022212,717 $256.97 
Granted (at market price) (1)
55,196 357.96 
Less: Vested58,705 172.24 
Forfeited
5,571 326.45 
Balance unvested at December 31, 2023203,637 $306.79 
Total restricted stock awards that vested for the past three years and related fair value
The table below presents the total number of restricted stock awards that vested for the past three years and the related fair value of those awards (in thousands, except share amounts):
 202320222021
Restricted stock awards - shares vested58,705 78,931 69,069 
Fair value of restricted stock awards vested$20,906 $37,258 $24,005 
Number of shares purchased by employees under the employee stock purchase plan For the two six month offering periods in each of the last three years, our employees purchased the following aggregate number of shares:
202320222021
7,640 7,658 8,649 
Restricted [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Summary of share-based compensation expense and recognized tax benefits [Table Text Block]
The following table presents the total share-based compensation expense for restricted stock awards for the past three years (in thousands):
 202320222021
Restricted stock awards share-based compensation expense$14,487 $11,024 $11,543 
Options [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Summary of share-based compensation expense and recognized tax benefits [Table Text Block]
The following table presents the total share-based compensation expense for stock option awards for the past three years (in thousands):
 202320222021
Option grants share-based compensation expense$4,618 $3,413 $2,846 
Option grants share-based compensation tax benefits1,154 853 712