Fair Value (Reconciliation For All Assets And Liabilities Measured At Fair Value On A Recurring Basis Using Significant Unobservable Inputs (Level 3)) (Details) - Fair Value, Inputs, Level 3 [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ (16,428)	$ (19,410)
Included in regulatory assets/liabilities	(1,660)	(2,671)
Settlements	5,115	3,118
Ending Balance	(12,973)	(18,963)
Natural Gas Exchange Agreements [Member]
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(3,164)	(5,885)
Included in regulatory assets/liabilities	203	2,012
Settlements	156	(405)
Ending Balance	(2,805)	(4,278)
Power Option Agreement [Member]
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(19)	(76)
Included in regulatory assets/liabilities	14	(190)
Settlements	0	0
Ending Balance	(5)	(266)
Power Exchange Agreements [Member]
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(13,245)	(13,449)
Included in regulatory assets/liabilities	(1,877)	(4,493)
Settlements	4,959	3,523
Ending Balance	$ (10,163)	$ (14,419)