Employee Benefit Plans (Schedule of Periodic Costs For Employee Retirement Benefit Plans) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Benefit Plan [Member]
Periodic costs for employee retirement benefit plans
Service Cost		$ 2,171	$ 2,426	$ 2,399
Interest Cost		3,426	3,061	3,143
Expected Return on Plan Assets		(4,694)	(4,871)	(4,489)
Amortization of Net Actuarial Loss		1,618	1,658	1,566
Amortization of Prior Service Credit
Net Periodic Benefit Cost	[1]	2,521	2,274	2,619
Other Benefits Plan [Member]
Periodic costs for employee retirement benefit plans
Service Cost		839	1,135	1,089
Interest Cost		1,984	1,898	1,964
Expected Return on Plan Assets		(2,451)	(2,550)	(2,406)
Amortization of Net Actuarial Loss		1,319	1,787	1,781
Amortization of Prior Service Credit			(1,607)	$ (1,728)
Net Periodic Benefit Cost	[1]	$ 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.