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Postretirement Benefit Plans (Net Periodic Benefit (Income) Costs) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Defined Benefit Postretirement Health And Life Coverage [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost $ 4 $ 4 $ 4
Interest cost 17 20 23
Amortization of prior service cost (25) (35) (35)
Amortization of net (gain) or loss (1)    
Net periodic postretirement benefit (income) cost (5) (11) (8)
Director's Retirement Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 36 35 34
Interest cost 38 43 46
Amortization of prior service cost 22 22 22
Net periodic postretirement benefit (income) cost 96 $ 100 $ 102
Defined Benefit Pension Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 287    
Interest cost 392    
Expected return on plan assets (423)    
Net periodic postretirement benefit (income) cost $ 256