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Stock-Based Compensation (Tables)
 12 Months Ended
Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Summary of the status of the Company's restricted stock shares A summary of the status of the Company’s restricted stock shares (restricted stock awards and restricted stock unit awards) as of December 31, 2018 and changes during the year ended December 31, 2018 is presented below:
 
Number of Shares
 
Weighted-Average
Grant Date Fair Value ($)
Outstanding at December 31, 2017
266,522

 
50.48

Granted
185,054

 
46.90

Vested
(141,089
)
 
51.09

Forfeited
(12,690
)
 
50.87

Outstanding at December 31, 2018
297,797

 
47.95
Market Condition Performance Share Awards  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Multiple input variables of performance share awards The inputs utilized for the performance share awards based on total shareholder return are as follows:
 
Weighted-Average at Grant Date for Twelve Months Ended December 31, 2018
 
Weighted-Average at Grant Date for Twelve Months Ended December 31, 2017
 
Expected volatility factor
0.39

 
0.40

 
Risk free interest rate
2.11

%
1.47

%
Expected term (in years)
2.96

 
2.93

 
Expected dividend yield
—

%
—

%
Performance share award activity The following table summarizes the Company’s market condition performance share awards for the year ended December 31, 2018:
 
Number of Awards
 
Weighted-Average Fair Value at Grant Date ($)
Outstanding at December 31, 2017
120,359

 
52.84

Granted
52,074

 
52.07

Vested
(83,977
)
 
50.88

Forfeited
(5,549
)
 
59.01

Outstanding at December 31, 2018
82,907

 
53.92
Performance Condition Performance Share Awards  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Performance share award activity The following table summarizes the Company’s performance condition performance share awards for the year ended December 31, 2018:
 
Number of Awards
 
Weighted-Average Fair Value at Grant Date ($)
Outstanding at December 31, 2017
35,507

 
45.72

Granted
26,037

 
46.21

Vested
(18,717
)
 
39.18

Forfeited
(1,373
)
 
51.04

Outstanding at December 31, 2018
41,454

 
49.81