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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, 2018
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Beginning balance 234,236 234,236
Exercised (2,484)  
Exercisable 231,752  
Outstanding, Weighted Average Exercise Price $ 34.97 $ 34.97
Exercised, Weighted Average Exercise Price 20.61  
Exercisable, Weighted Average Exercise Price $ 35.13  
Exercisable, Average Remaining Contractual Term Years 4 years 22 days 5 years 11 days
Outstanding, Aggregate Intrinsic Value $ 7,291 $ 7,291
Exercisable, Aggregate Intrinsic Value $ 5,651