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Employee Benefit Plans (Schedule of Periodic Costs For Employee Retirement Benefit Plans) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Pension Benefit Plan [Member]      
Periodic costs for employee retirement benefit plans      
Service Cost $ 2,434 $ 2,171 $ 2,426
Interest Cost 3,099 3,426 3,061
Expected Return on Plan Assets (5,635) (4,694) (4,871)
Amortization of Net Actuarial Loss 2,059 1,618 1,658
Amortization of Prior Service Credit
Net Periodic Benefit Cost [1] 1,957 2,521 2,274
Other Benefits Plan [Member]      
Periodic costs for employee retirement benefit plans      
Service Cost 993 839 1,135
Interest Cost 1,699 1,984 1,898
Expected Return on Plan Assets (2,853) (2,451) (2,550)
Amortization of Net Actuarial Loss 1,352 1,319 1,787
Amortization of Prior Service Credit (1,607)
Net Periodic Benefit Cost [1] $ 1,191 $ 1,691 $ 663
[1] Service cost is included in Operations and Maintenance expense on the consolidated statements of income; all other amounts are included in Other Income (Expense), net.