Financial Instruments (Schedule Of Derivatives And Hedged Items In Fair Value Hedging Relationships) (Details) $ in Thousands	6 Months Ended
	Mar. 31, 2017 USD ($)
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) on Derivative Recognized in the Consolidated Statement of Income	$ 3,180
Amount of Gain or (Loss) on the Hedged Item Recognized in the Consolidated Statement of Income	(3,180)
Operating Revenues [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) on Derivative Recognized in the Consolidated Statement of Income	2,954
Amount of Gain or (Loss) on the Hedged Item Recognized in the Consolidated Statement of Income	(2,954)
Purchased Gas [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) on Derivative Recognized in the Consolidated Statement of Income	226
Amount of Gain or (Loss) on the Hedged Item Recognized in the Consolidated Statement of Income	$ (226)