Employee Benefit Plans (Schedule of Benefits Plans) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension Benefit Plan [Member]
Periodic costs for employee retirement benefit plans
Service Cost		$ 609	$ 543	$ 1,826	$ 1,628
Interest Cost		775	857	2,324	2,570
Expected Return on Assets		(1,409)	(1,173)	(4,226)	(3,520)
Amortization of Unrecognized Losses		515	404	1,544	1,213
Net Periodic Benefit Cost	[1]	490	631	1,468	1,891
Other Benefits Plan [Member]
Periodic costs for employee retirement benefit plans
Service Cost		248	210	745	630
Interest Cost		425	496	1,274	1,488
Expected Return on Assets		(721)	(613)	(2,163)	(1,838)
Amortization of Unrecognized Losses		338	330	1,014	989
Net Periodic Benefit Cost	[1]	$ 290	$ 423	$ 870	$ 1,269

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