Summary Of Significant Accounting Policies (Reclassification Out Of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Operating Revenues	$ 551,115	$ 491,095	$ 992,275	$ 935,283
Purchased Gas	106,661	118,270	158,280	210,542
Other Income (Deductions)	(10,875)	(17,480)	(13,051)	(20,520)
Income (Loss) Before Income Taxes	152,646	(69,222)	259,837	48,764
Income Tax Expense	(40,210)	(36,846)	(69,627)	(68,241)
Net Income (Loss) Available for Common Stock	112,436	(106,068)	190,210	(19,477)
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	(3,666)	25,034	(3,977)	32,386
Income Tax Expense	1,010	(6,817)	1,096	(8,849)
Net Income (Loss) Available for Common Stock	(2,656)	18,217	(2,881)	23,537
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	(3,761)	23,396	(4,071)	30,937
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	0	1,909	0	1,911
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	$ 95	$ (271)	$ 94	$ (462)