Employee Benefit Plans (Schedule of Benefits Plans) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Pension Benefit Plan [Member]
Periodic costs for employee retirement benefit plans
Service Cost		$ 674	$ 609	$ 1,348	$ 1,217
Interest Cost		677	775	1,353	1,550
Expected Return on Assets		(1,556)	(1,409)	(3,114)	(2,818)
Amortization of Unrecognized Losses		717	515	1,434	1,030
Net Periodic Benefit Cost (Benefit)	[1]	512	490	1,021	979
Other Benefits Plan [Member]
Periodic costs for employee retirement benefit plans
Service Cost		229	248	458	497
Interest Cost		309	425	618	850
Expected Return on Assets		(786)	(721)	(1,571)	(1,442)
Amortization of Unrecognized Losses		132	338	264	676
Net Periodic Benefit Cost (Benefit)	[1]	$ (116)	$ 290	$ (231)	$ 581

[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.