Summary Of Significant Accounting Policies (Reclassification Out Of Accumulated Other Comprehensive Loss) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Operating Revenues	$ 440,144	$ 440,008	$ 1,746,458	$ 1,490,688
Purchased Gas	(86,628)	(95,164)	(577,005)	(426,900)
Other Income	1,496	1,163	6,847	3,666
Income Before Income Taxes	105,627	104,183	404,610	356,582
Income Tax Expense	(41,107)	(45,688)	(162,627)	(144,423)
Net Income Available for Common Stock	64,520	58,495	241,983	212,159
Amount Of Gain Or (Loss) Reclassified From Accumulated Other Comprehensive Loss [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income Before Income Taxes	(14,480)		(30,937)
Income Tax Expense	8,269		15,141
Net Income Available for Common Stock	(6,211)		(15,796)
Amount Of Gain Or (Loss) Reclassified From Accumulated Other Comprehensive Loss [Member] | Gains and Losses on Securities Available for Sale [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other Income	(16)		(16)
Amount Of Gain Or (Loss) Reclassified From Accumulated Other Comprehensive Loss [Member] | Commodity Contracts [Member] | Gains And Losses On Derivative Financial Instruments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Operating Revenues	(14,547)		(27,372)
Purchased Gas	$ 83		$ (3,549)