Summary Of Significant Accounting Policies (Reclassification Out Of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Loss [Line Items]
Operating Revenues	$ 552,544	$ 540,905	$ 1,042,791	$ 960,561
Other Income (Deductions)	(5,919)	(13,092)	(15,521)	(16,594)
Income Before Income Taxes	120,380	130,116	245,949	247,494
Income Tax Expense	(29,785)	(38,269)	(52,693)	43,007
Net Income Available for Common Stock	90,595	91,847	193,256	290,501
Amount Of Gain Or (Loss) Reclassified From Accumulated Other Comprehensive Loss [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Loss [Line Items]
Income Before Income Taxes	(4,739)	(3,199)	(24,384)	9,779
Income Tax Expense	1,328	551	6,874	(4,804)
Net Income Available for Common Stock	(3,411)	(2,648)	(17,510)	4,975
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 Loss [Line Items]
Other Income (Deductions)	0	0	0	430
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 Loss [Line Items]
Operating Revenues	(4,260)	(3,467)	(22,782)	9,375
Foreign Currency Contracts [Member] | Amount Of Gain Or (Loss) Reclassified From Accumulated Other Comprehensive Loss [Member] | Gains And Losses On Derivative Financial Instruments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Loss [Line Items]
Operating Revenues	(199)	(482)	(420)	(973)
Purchased Gas [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Loss [Line Items]
Purchased Gas	195,037	176,608	333,697	270,642
Purchased Gas [Member] | 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 Loss [Line Items]
Purchased Gas	$ (280)	$ 750	$ (1,182)	$ 947