Employee Benefit Plans (Schedule of Benefits Plans) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Pension Benefit Plan [Member]
Periodic costs for employee retirement benefit plans
Service Cost		$ 609	$ 543
Interest Cost		775	857
Expected Return on Assets		(1,409)	(1,173)
Amortization of Unrecognized Losses		515	404
Net Periodic Benefit Cost	[1]	490	631
Other Benefits Plan [Member]
Periodic costs for employee retirement benefit plans
Service Cost		248	210
Interest Cost		425	496
Expected Return on Assets		(721)	(613)
Amortization of Unrecognized Losses		338	330
Net Periodic Benefit Cost	[1]	$ 290	$ 423

[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.