Employee Benefit Plans (Schedule of Benefits Plans) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Pension Benefit Plan [Member]
Periodic costs for employee retirement benefit plans
Service Cost		$ 543	$ 607	$ 1,085	$ 1,213
Interest Cost		857	765	1,713	1,530
Expected Return on Assets		(1,173)	(1,218)	(2,347)	(2,435)
Amortization of Unrecognized Losses		404	415	809	829
Amortization of Unrecognized Prior Service Cost (Credit)
Net Periodic Benefit Cost	[1]	631	569	1,260	1,137
Other Benefits Plan [Member]
Periodic costs for employee retirement benefit plans
Service Cost		210	284	420	567
Interest Cost		496	474	992	949
Expected Return on Assets		(613)	(637)	(1,226)	(1,275)
Amortization of Unrecognized Losses		330	447	660	894
Amortization of Unrecognized Prior Service Cost (Credit)			(402)		(803)
Net Periodic Benefit Cost	[1]	$ 423	$ 166	$ 846	$ 332

[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.