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Equity Compensation Plans (Weighted Average Estimated Grant Date Fair Value Per Share of Stock Options and Restricted Stock Granted) (Details) - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted average estimated grant date fair value per share of the stock options granted $ 8.60 $ 8.25 $ 11.12
Restricted Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted average estimated grant date fair value per share of the restricted stock granted $ 19.38 $ 16.35 $ 17.82