Summary Of Significant Accounting Policies (Reclassification Out Of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Operating Revenues	$ 339,815	$ 440,144	$ 1,459,851	$ 1,746,458
Purchased Gas	(27,038)	(86,628)	(344,728)	(577,005)
Other Income	2,066	1,496	4,638	6,847
Income Before Income Taxes	(510,041)	105,627	(348,334)	404,610
Income Tax Expense	216,907	(41,107)	156,610	(162,627)
Net Income (Loss) Available for Common Stock	(293,134)	64,520	(191,724)	241,983
Amount Of Gain Or (Loss) Reclassified From Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income Before Income Taxes	50,875	(14,480)	129,270	(30,937)
Income Tax Expense	(21,800)	8,269	(54,807)	15,141
Net Income (Loss) Available for Common Stock	29,075	(6,211)	74,463	(15,796)
Amount Of Gain Or (Loss) Reclassified From Accumulated Other Comprehensive Income (Loss) [Member] | Gains (Losses) on Securities Available for Sale [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other Income	0	(16)	0	(16)
Amount Of Gain Or (Loss) Reclassified From Accumulated Other Comprehensive Income (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	50,878	(14,547)	124,386	(27,372)
Purchased Gas	$ (3)	$ 83	$ 4,884	$ (3,549)