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Stock-Based Compensation (Summary of Company's SARs Activity) (Details) - SARs [Member] - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 12 Months Ended
Mar. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Beginning balance 237,121  
Exercised (11,335)  
Ending balance   237,121
Exercisable 225,786  
Beginning balance, Weighted Average Exercise Price $ 29.86  
Exercised, Weighted Average Exercise Price 21.95  
Ending balance, Weighted Average Exercise Price   $ 29.86
Exercisable, Weighted Average Exercise Price $ 30.26  
Beginning balance, Average Remaining Contractual Term Years   3 years 6 months
Exercisable, Average Remaining Contractual Term Years 3 years 3 months 29 days  
Beginning balance, Aggregate Intrinsic Value $ 5,468  
Ending balance, Aggregate Intrinsic Value   $ 5,468
Exercisable, Aggregate Intrinsic Value $ 3,848