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Retirement Plans (Weighted-Average Expense Assumptions) (Details)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Discount rate 3.46%    
Expected return on plan assets 6.36%    
Retirement Income Plan [Member]      
Discount rate 4.41% 4.69% 4.29%
Expected return on plan assets 6.24% 6.37% 6.27%
Rate of compensation increase [1] 0.00% 0.00% 4.00%
Discount rate used to value the liability 3.78% 4.41%  
[1] This assumption was 4.00% through March 31, 2016, the date after which benefits ceased accruing for all participants of the Pension Plan.