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		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ (18,963)	$ (26,296)	$ (19,410)	$ (27,124)
Included in regulatory assets/liabilities	(644)	2,841	(3,315)	(1,309)
Settlements	1,607	1,879	4,725	6,857
Ending Balance	(18,000)	(21,576)	(18,000)	(21,576)
Natural Gas Exchange Agreements [Member]
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(4,278)	(6,006)	(5,885)	(5,039)
Included in regulatory assets/liabilities	(195)	(1,551)	1,817	(3,296)
Settlements	300	700	(105)	1,478
Ending Balance	(4,173)	(6,857)	(4,173)	(6,857)
Power Option Agreement [Member]
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(266)	(97)	(76)	(124)
Included in regulatory assets/liabilities	223	(8)	33	19
Settlements	0	0	0	0
Ending Balance	(43)	(105)	(43)	(105)
Power Exchange Agreements [Member]
Fair Value Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(14,419)	(20,193)	(13,449)	(21,961)
Included in regulatory assets/liabilities	(672)	4,400	(5,165)	1,968
Settlements	1,307	1,179	4,830	5,379
Ending Balance	$ (13,784)	$ (14,614)	$ (13,784)	$ (14,614)