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Stock-Based Compensation
 6 Months Ended
Jun. 30, 2019
Share-based Payment Arrangement [Abstract]  
Stock-Based Compensation
16.
Stock–Based Compensation
The Company regularly grants equity awards under its stockholder-approved equity plans to certain employees and directors. The fair value of equity awards granted during the six months ended June 30, 2019 and 2018 totaled $45.2 million and $30.1 million, respectively. The fair value of restricted stock units, deferred stock units and performance based restricted stock
units is based on the closing market price of the Company’s stock on the grant date as reported by the NYSE. The fair value of each service-based stock option award is estimated on the grant date using a Black-Scholes-Merton option-pricing model.
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
%