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Employee Benefit Plans (Changes in Accumulated Postretirement Benefits Obligations) (Details) - Postretirement Medical and Life Benefit Plan - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]      
Obligation at the Beginning of Year $ 1,498 $ 1,154  
Unrecognized Loss (Gain) 114 296  
Components of Net Periodic Postretirement Benefit Cost      
Service Cost 110 83 $ 69
Interest Cost 41 43 34
Net Expected Benefit Payments (96) (92)  
Amendments (33) 14  
Obligation at End of Year $ 1,634 $ 1,498 $ 1,154