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, 2016	Mar. 31, 2015
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ (27,124)	$ (23,758)
Included in regulatory assets/liabilities	(4,150)	(5,431)
Settlements	4,978	3,852
Ending Balance	(26,296)	(25,337)
Natural Gas Exchange Agreements [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Ending Balance		817
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(5,039)	(35)
Included in regulatory assets/liabilities	(1,745)	777
Settlements	778	75
Ending Balance	(6,006)
Power Option Agreement [Member]
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(124)	(424)
Included in regulatory assets/liabilities	27	173
Settlements	0	0
Ending Balance	(97)	(251)
Power Exchange Agreements [Member]
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(21,961)	(23,299)
Included in regulatory assets/liabilities	(2,432)	(6,381)
Settlements	4,200	3,777
Ending Balance	$ (20,193)	$ (25,903)