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		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ (18,000)	$ (21,576)	$ (19,410)	$ (27,124)
Included in regulatory assets/liabilities	(2,222)	(2,052)	(5,537)	(3,361)
Settlements	(43)	0	4,682	6,857
Ending Balance	(20,265)	(23,628)	(20,265)	(23,628)
Natural Gas Exchange Agreements [Member]
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(4,173)	(6,857)	(5,885)	(5,039)
Included in regulatory assets/liabilities	617	336	2,434	(2,960)
Settlements	(43)	0	(148)	1,478
Ending Balance	(3,599)	(6,521)	(3,599)	(6,521)
Power Option Agreement [Member]
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(43)	(105)	(76)	(124)
Included in regulatory assets/liabilities	31	(692)	64	(673)
Settlements	0	0	0	0
Ending Balance	(12)	(797)	(12)	(797)
Power Exchange Agreements [Member]
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(13,784)	(14,614)	(13,449)	(21,961)
Included in regulatory assets/liabilities	(2,870)	(1,696)	(8,035)	272
Settlements	0	0	4,830	5,379
Ending Balance	$ (16,654)	$ (16,310)	$ (16,654)	$ (16,310)