Financial Instruments (Schedule of Derivatives and Hedged Items in Fair Value Hedging Relationships') (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Dec. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (Loss) on the Derivative Recognized in the Consolidated Statement of Income	$ (1,605)
Amount of Gain or (Loss) on the Hedged Item Recognized in the Consolidated Statement of Income	1,605
Operating Revenues [Member] | Fixed Price Sales Commitments Of Natural Gas [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (Loss) on the Derivative Recognized in the Consolidated Statement of Income	(1,678)
Amount of Gain or (Loss) on the Hedged Item Recognized in the Consolidated Statement of Income	1,678
Purchased Gas [Member] | Fixed Price Purchase Commitments Of Natural Gas [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (Loss) on the Derivative Recognized in the Consolidated Statement of Income	9
Amount of Gain or (Loss) on the Hedged Item Recognized in the Consolidated Statement of Income	(9)
Purchased Gas [Member] | Natural Gas Held in Storage [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain or (Loss) on the Derivative Recognized in the Consolidated Statement of Income	64
Amount of Gain or (Loss) on the Hedged Item Recognized in the Consolidated Statement of Income	$ (64)