Consolidated Statements Of Income And Earnings Reinvested In The Business - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
INCOME
Operating Revenues	$ 1,546,291	$ 1,693,332	$ 1,592,668
Operating Expenses:
Purchased Gas	233,890	386,265	337,822
Property, Franchise and Other Taxes	88,400	88,886	84,393
Depreciation, Depletion and Amortization	306,158	275,660	240,961
Impairment of Oil and Gas Producing Properties	449,438	0	0
Total Operating Expenses	1,516,433	1,181,523	1,072,945
Operating Income	29,858	511,809	519,723
Other Income (Expense):
Other Income (Deductions)	(17,814)	(15,542)	(21,174)
Interest Expense on Long-Term Debt	(110,012)	(101,614)	(110,946)
Other Interest Expense	(7,065)	(5,142)	(3,576)
Income (Loss) Before Income Taxes	(105,033)	389,511	384,027
Income Tax Expense (Benefit)	18,739	85,221	(7,494)
Net Income (Loss) Available for Common Stock	(123,772)	304,290	391,521
EARNINGS REINVESTED IN THE BUSINESS
Balance at Beginning of Year	1,272,601	1,098,900	851,669
Beginning Retained Earnings Unappropriated And Current Period Net Income	1,148,829	1,403,190	1,243,190
Dividends on Common Stock	(156,249)	(148,432)	(144,290)
Balance at End of Year	$ 991,630	$ 1,272,601	$ 1,098,900
Earnings (Loss) Per Common Share, Basic:
Net Income (Loss) Available for Common Stock (in dollars per share)	$ (1.41)	$ 3.53	$ 4.56
Earnings (Loss) Per Common Share, Diluted:
Net Income (Loss) Available for Common Stock (in dollars per share)	$ (1.41)	$ 3.51	$ 4.53
Weighted Average Number of Shares Outstanding:
Used in Basic Calculation	87,968,895	86,235,550	85,830,597
Used in Diluted Calculation	87,968,895	86,773,259	86,439,698
Utility and Energy Marketing [Member]
INCOME
Operating Revenues	$ 728,336	$ 860,985	$ 812,474
Operating Expenses:
Operation and Maintenance	181,051	171,472	168,885
Exploration and Production and Other [Member]
INCOME
Operating Revenues	611,885	636,528	569,808
Operating Expenses:
Operation and Maintenance	148,856	147,457	139,546
Pipeline and Storage and Gathering [Member]
INCOME
Operating Revenues	206,070	195,819	210,386
Operating Expenses:
Operation and Maintenance	108,640	111,783	101,338
Guidance for Hedging [Member] | Cumulative Effect of Adoption of Authoritative Guidance [Member]
EARNINGS REINVESTED IN THE BUSINESS
Balance at Beginning of Year	(950)	0	0
Balance at End of Year		(950)	0
Guidance for Recognition and Measurement of Financial Assets and Liabilities [Member] | Cumulative Effect of Adoption of Authoritative Guidance [Member]
EARNINGS REINVESTED IN THE BUSINESS
Balance at Beginning of Year	0	7,437	0
Balance at End of Year		0	7,437
Guidance for Reclassification of Stranded Tax Effects [Member] | Cumulative Effect of Adoption of Authoritative Guidance [Member]
EARNINGS REINVESTED IN THE BUSINESS
Balance at Beginning of Year	$ 0	10,406	0
Balance at End of Year		$ 0	$ 10,406