Employee Benefit Plans (Schedule of Benefits Plans) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Pension Benefit Plan [Member]
Periodic costs for employee retirement benefit plans
Service Cost		$ 674	$ 609
Interest Cost		677	775
Expected Return on Assets		(1,556)	(1,409)
Amortization of Unrecognized Losses		717	515
Net Periodic Benefit Cost (Benefit)	[1]	512	490
Other Benefits Plan [Member]
Periodic costs for employee retirement benefit plans
Service Cost		229	248
Interest Cost		309	425
Expected Return on Assets		(786)	(721)
Amortization of Unrecognized Losses		132	338
Net Periodic Benefit Cost (Benefit)	[1]	$ (116)	$ 290

[1] Service cost is included in Operations and Maintenance expense on the Condensed Consolidated Statements of Income; all other amounts are included in Other Income/Expense, net.