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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Operating Revenues	$ 348,368	$ 335,617	$ 1,292,944	$ 1,159,943
Purchased Gas	46,135	23,477	264,349	147,168
Other Income	1,370	1,519	4,728	7,173
Income Before Income Taxes	95,506	17,026	383,101	(580,151)
Income Tax Expense	(35,792)	(8,740)	(145,195)	251,641
Net Income (Loss) Available for Common Stock	59,714	8,286	237,906	(328,510)
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	18,452	58,373	60,382	177,167
Income Tax Expense	(7,693)	(24,514)	(25,333)	(68,283)
Net Income (Loss) Available for Common Stock	10,759	33,859	35,049	108,884
Amount Of Gain Or (Loss) Reclassified From Accumulated Other Comprehensive Income (Loss) [Member] | Gains And Losses On Securities Available For Sale [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other Income	0	0	741	388
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	18,600	58,354	62,030	172,596
Purchased Gas	21	70	(1,938)	4,520
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 [Line Items]
Operation and Maintenance	$ (169)	$ (51)	$ (451)	$ (337)