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, 2017	Mar. 31, 2016
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ (19,410)	$ (27,124)
Included in regulatory assets/liabilities	(2,671)	(4,150)
Settlements	3,118	4,978
Ending Balance	(18,963)	(26,296)
Natural Gas Exchange Agreements [Member]
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(5,885)	(5,039)
Included in regulatory assets/liabilities	2,012	(1,745)
Settlements	(405)	778
Ending Balance	(4,278)	(6,006)
Power Option Agreement [Member]
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(76)	(124)
Included in regulatory assets/liabilities	(190)	27
Settlements	0	0
Ending Balance	(266)	(97)
Power Exchange Agreements [Member]
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(13,449)	(21,961)
Included in regulatory assets/liabilities	(4,493)	(2,432)
Settlements	3,523	4,200
Ending Balance	$ (14,419)	$ (20,193)