Fair Value (Reconciliation For All Assets And Liabilities Measured At Fair Value On A Recurring Basis Using Significant Unobservable Inputs (Level 3)) (Details) - Level 3 [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ (9,825)	$ (17,957)	$ (16,409)	$ (19,334)
Included in regulatory assets/liabilities	912	(2,253)	1,067	(5,601)
Settlements	0	(43)	6,429	4,682
Ending Balance	(8,913)	(20,253)	(8,913)	(20,253)
Natural Gas Exchange Agreements [Member]
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(3,480)	(4,173)	(3,164)	(5,885)
Included in regulatory assets/liabilities	476	617	(89)	2,434
Settlements	0	(43)	249	(148)
Ending Balance	(3,004)	(3,599)	(3,004)	(3,599)
Power Exchange Agreements [Member]
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(6,345)	(13,784)	(13,245)	(13,449)
Included in regulatory assets/liabilities	436	(2,870)	1,156	(8,035)
Settlements	0	0	6,180	4,830
Ending Balance	$ (5,909)	$ (16,654)	$ (5,909)	$ (16,654)