Derivatives And Hedging (Schedule Of Derivative Instruments On The Statement Of Revenues, Expenses, And Patronage Capital) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Regulatory Asset/Liability for Derivatives	$ 7,005	$ (3,694)
Amount Of Gain (Loss) Reclassified from Regulatory Asset/Liability into Income	(2,369)	(6,667)
Natural Gas Future Contracts [Member] | Fuel [Member] | Operating Expense Fuel [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Recognized in Regulatory Asset/Liability for Derivatives	7,005	(3,694)
Amount Of Gain (Loss) Reclassified from Regulatory Asset/Liability into Income	$ (2,369)	(6,653)
Energy Related Derivative [Member] | Purchased Power Contracts [Member] | Operating Expense Purchased Power [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount Of Gain (Loss) Reclassified from Regulatory Asset/Liability into Income		$ (14)