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Stock-Based Compensation (Tables)
 12 Months Ended
Dec. 31, 2018
Share-based Compensation [Abstract]  
Target grants performance share Target grants of performance shares outstanding at December 31, 2018, were as follows:
Grant Date
Performance
Period
Target Grant
of Shares

February 2016
2016-2018
255,773

March 2016
2016-2018
2,151

February 2017
2017-2019
164,558

February 2018
2018-2020
246,309
Schedule of share-based payment award, performance shares, valuation assumptions Assumptions used for grants applicable to the market condition for certain performance shares issued in 2018, 2017 and 2016 were:
 
 
 
2018

 
 
2017

 
 
2016

Weighted average grant-date fair value
 
 

$34.55

 
 

$24.31

 
 

$14.60

Blended volatility range
17.87
%
–
22.14
%
22.70
%
–
25.56
%
29.25
%
–
32.51
%
Risk-free interest rate range
1.86
%
–
2.46
%
.69
%
–
1.61
%
.47
%
–
.92
%
Weighted average discounted dividends per share
 
 

$2.46

 
 

$1.70

 
 

$1.56
Summary of the status of the performance share awards A summary of the status of the performance share awards for the year ended December 31, 2018, was as follows:
 
Number of
Shares

Weighted
Average
Grant-Date
Fair Value

Nonvested at beginning of period
425,534

$
18.35

Granted
246,309

31.02

Less:
 
 
Forfeited
3,052

14.60

Nonvested at end of period
668,791

$
23.03