Pension Plans And Other Postretirement Benefit Plans (Components Of Net Periodic Benefit Cost) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Percentage of Net Periodic Benefit Costs Capitalized to Utility Property			40.00%
Percentage of Net Periodic Benefit Costs Recorded to Operating Expenses			60.00%
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5,092	$ 4,567	$ 15,226	$ 13,655
Interest cost	6,976	6,895	20,903	20,695
Expected return on plan assets	(7,900)	(6,887)	(23,700)	(20,512)
Amortization of prior service cost	0	1	0	1
Net loss recognition	2,517	2,161	7,380	6,252
Net periodic benefit cost	6,685	6,737	19,809	20,091
Other Post-Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	799	806	2,422	2,389
Interest cost	1,374	1,530	4,147	4,623
Expected return on plan assets	(475)	(465)	(1,425)	(1,415)
Amortization of prior service cost	(274)	(300)	(898)	(924)
Net loss recognition	1,168	1,453	3,761	4,312
Net periodic benefit cost	$ 2,592	$ 3,024	$ 8,007	$ 8,985