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Stock Incentive Plan Summary of Options by Range of Exercise Price (Details) - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]        
Weighted-Average Exercise Price $ 23.00 $ 24.65 $ 24.67 $ 24.64
$22.50 to $24.50        
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]        
Number Outstanding 10,500      
Weighted-Average Remaining Contractual Life 350 days      
Weighted-Average Exercise Price $ 23.00      
Number Exercisable 10,500      
Weighted-Average Exercise Price $ 23.00