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Pension and Postretirement Benefit Plans (Narrative) (Details)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
USD ($)
employee
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Defined Benefit Plan Disclosure [Line Items]      
Retired employees receiving health care and life insurance benefits | employee 9    
Post retirement benefits, age eligibility requirement 65 years    
Post retirement benefits, service eligibility requirement 15 years    
Unrecognized net actuarial gain $ 44    
Recognized transition obligation $ 7    
Annual rate of increase in cost of covered health care benefits, next fiscal year 8.00%    
Annual rate of increase in cost of covered health care benefits, two fiscal years 8.00%    
Annual rate of increase in cost of covered health care benefits, three fiscal years 7.00%    
Annual rate of increase in cost of covered health care benefits, four fiscal years 7.00%    
Annual rate of increase in cost of covered health care benefits, five fiscal years and thereafter 5.00%    
Postretirement Benefits Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Net periodic benefit cost $ (4) $ (2) $ (2)
Unrecognized net actuarial gain $ 4 $ 7 $ 6
Benefit obligation weighted average discount rate 2.75% 3.00% 3.25%
Effect of 1% rate increase on benefit obligation $ 3    
Effect of 1% rate increase on net periodic benefit cost (less than one thousand) 1    
Effect of 1% rate decrease on benefit obligation (3)    
Effect of 1% rate decrease on net periodic benefit cost (less than one thousand) $ 1