Summary Of Significant Accounting Policies (Reclassification Out Of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Loss [Line Items]
Operating Revenues	$ 342,912	$ 348,368	$ 1,303,473	$ 1,292,944
Other Income	999	1,370	3,492	4,728
Income Before Income Taxes	82,208	95,506	329,702	383,101
Income Tax Expense	(19,183)	(35,792)	23,825	(145,195)
Net Income Available for Common Stock	63,025	59,714	353,527	237,906
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	(3,771)	18,452	6,007	60,382
Income Tax Expense	1,208	(7,693)	(3,596)	(25,333)
Net Income Available for Common Stock	(2,563)	10,759	2,411	35,049
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	0	0	430	741
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	(3,249)	18,600	6,125	62,030
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]
Operation and Maintenance	(527)	(169)	(1,500)	(451)
Purchased Gas [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Loss [Line Items]
Purchased Gas	52,211	46,135	322,854	264,349
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	$ 5	$ 21	$ 952	$ (1,938)