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	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ (19,410)	$ (27,124)	$ (23,758)	$ (16,435)
Included in regulatory assets/liabilities	707	(11,906)	(5,778)
Settlements	7,007	8,540	(1,545)
Natural Gas Exchange Agreements [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	(5,885)	(5,039)	(35)	(1,219)
Included in regulatory assets/liabilities	259	(6,008)	3,873
Settlements	(1,105)	1,004	(2,689)
Power Exchange Agreements [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	(13,449)	(21,961)	(23,299)	(14,441)
Included in regulatory assets/liabilities	400	(6,198)	(10,002)
Settlements	8,112	7,536	1,144
Commodity Option [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	(76)	(124)	(424)	$ (775)
Included in regulatory assets/liabilities	48	300	351
Settlements	$ 0	$ 0	$ 0