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Stock-Based Compensation (Tables)
6 Months Ended
Jun. 30, 2019
Share-based Payment Arrangement [Abstract]  
Schedule of Assumptions Used
The table below presents the weighted average fair value of service-based stock options by year of grant and the assumptions used in estimating those fair values:
 
 
2019
 
2018
Weighted average grant date fair value
 
$
58.28

 
$
51.27

 
 
 
 
 
Weighted average expected life (in years)
 
6.0

 
6.0

Weighted average exercise price
 
$
184.81

 
$
158.23

Expected stock price volatility
 
27.21
%
 
27.35
%
Risk-free interest rate
 
2.37
%
 
2.69
%