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Stock-Based Compensation (Tables)
 9 Months Ended
Sep. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Schedule of Assumptions Used
The table below summarizes the assumptions used to calculate the fair value of service-based stock options by year of grant:
 
 
2018
 
2017
Weighted average expected life (in years)
 
6.0

 
6.0

Weighted average exercise price
 
$
158.23

 
$
104.95

Expected stock price volatility
 
27.35
%
 
30.67
%
Risk-free interest rate
 
2.69
%
 
2.13
%
Weighted average fair value
 
$
51.27

 
$
35.58