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Defined Pension Plans (Narrative) (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Defined Benefit Plan Disclosure [Line Items]        
Pension costs      
Pension period     30 years  
Defined Benefit Pension Plan [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Pension costs $ 1,049 $ 1,017 $ 2,098 2,037
Unfunded Supplemental Executive Retirement Plan [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Pension costs $ 256 $ 209 $ 511 $ 418