Summary Of Significant Accounting Policies (Reclassification Out of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands		3 Months Ended												12 Months Ended
		Sep. 30, 2020		Jun. 30, 2020		Mar. 31, 2020		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating Revenues		$ 287,989		$ 323,019		$ 491,095		$ 444,188	$ 293,341	$ 357,200	$ 552,544	$ 490,247		$ 1,546,291	$ 1,693,332	$ 1,592,668
Other Income (Deductions)														(17,814)	(15,542)	(21,174)
Purchased Gas														233,890	386,265	337,822
Income (Loss) Before Income Taxes														(105,033)	389,511	384,027
Income Tax Expense														(18,739)	(85,221)	7,494
Net Income (Loss) Available for Common Stock		$ (145,545)	[1]	$ 41,250	[2]	$ (106,068)	[3]	$ 86,591	$ 47,282	$ 63,753	$ 90,595	$ 102,660	[4]	(123,772)	304,290	$ 391,521
Amount Of Gain Or (Loss) Reclassified From Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Income (Loss) Before Income Taxes														77,934	(12,796)
Income Tax Expense														(21,955)	4,424
Net Income (Loss) Available for Common Stock														55,979	(8,372)
Amount Of Gain Or (Loss) Reclassified From Accumulated Other Comprehensive Income (Loss) [Member] | Amortization of Prior Year Funded Status of Pension and Other Post-Retirement Benefit Plans [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Amortization of Prior Service Cost	[5]													(237)	(264)
Recognition of Net Actuarial Loss	[5]													(15,124)	(7,068)
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 (Loss) [Line Items]
Operating Revenues															(3,460)
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 (Loss) [Line Items]
Operating Revenues														93,691
Foreign Currency Contracts [Member] | Amount Of Gain Or (Loss) Reclassified From Accumulated Other Comprehensive Income (Loss) [Member] | Gains and Losses on Derivative Financial Instruments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating Revenues															(822)
Foreign Currency Contracts [Member] | Amount Of Gain Or (Loss) Reclassified From Accumulated Other Comprehensive Income (Loss) [Member] | Gains and Losses on Derivative Financial Instruments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating Revenues														(1,057)
Purchased Gas [Member] | 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 (Loss) [Line Items]
Purchased Gas															$ (1,182)
Purchased Gas [Member] | 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 (Loss) [Line Items]
Purchased Gas														$ 661

[1] Includes a non-cash $253.4 million impairment charge ($183.7 million after tax) associated with the Exploration and Production segment's oil and gas producing properties.

[2] Includes a non-cash $18.2 million impairment charge ($13.3 million after tax) associated with the Exploration and Production segment's oil and gas producing properties.

[3] Includes a non-cash $177.8 million impairment charge ($129.3 million after tax) associated with the Exploration and Production segment's oil and gas producing properties and a $56.8 million valuation allowance recorded against certain deferred tax assets.

[4] Includes a $5.0 million reduction to income tax expense associated with the remeasurement of accumulated deferred income taxes in accordance with the 2017 Tax Reform Act.

[5] These accumulated other comprehensive income (loss) components are included in the computation of net periodic benefit cost. Refer to Note K — Retirement Plan and Other Post-Retirement Benefits for additional details.