Consolidated Statements Of Income And Earnings Reinvested In The Business - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
INCOME
Operating Revenues	$ 1,742,659	$ 1,546,291	$ 1,693,332
Operating Expenses:
Purchased Gas	171,827	233,890	386,265
Property, Franchise and Other Taxes	94,713	88,400	88,886
Depreciation, Depletion and Amortization	335,303	306,158	275,660
Impairment of Oil and Gas Producing Properties	76,152	449,438	0
Total Operating Expenses	1,153,801	1,516,433	1,181,523
Gain on Sale of Timber Properties	51,066	0	0
Operating Income	639,924	29,858	511,809
Other Income (Expense):
Other Income (Deductions)	(15,238)	(17,814)	(15,542)
Interest Expense on Long-Term Debt	(141,457)	(110,012)	(101,614)
Other Interest Expense	(4,900)	(7,065)	(5,142)
Income (Loss) Before Income Taxes	478,329	(105,033)	389,511
Income Tax Expense	114,682	18,739	85,221
Net Income (Loss) Available for Common Stock	363,647	(123,772)	304,290
EARNINGS REINVESTED IN THE BUSINESS
Balance at Beginning of Year	991,630	1,272,601	1,098,900
Beginning Retained Earnings Unappropriated And Current Period Net Income	1,355,277	1,148,829	1,403,190
Dividends on Common Stock	(164,102)	(156,249)	(148,432)
Balance at End of Year	$ 1,191,175	$ 991,630	$ 1,272,601
Earnings (Loss) Per Common Share, Basic:
Net Income (Loss) Available for Common Stock (in dollars per share)	$ 3.99	$ (1.41)	$ 3.53
Earnings (Loss) Per Common Share, Diluted:
Net Income (Loss) Available for Common Stock (in dollars per share)	$ 3.97	$ (1.41)	$ 3.51
Weighted Average Number of Shares Outstanding:
Used in Basic Calculation	91,130,941	87,968,895	86,235,550
Used in Diluted Calculation	91,684,583	87,968,895	86,773,259
Utility and Energy Marketing [Member]
INCOME
Operating Revenues	$ 667,549	$ 728,336	$ 860,985
Operating Expenses:
Operation and Maintenance	179,547	181,051	171,472
Exploration and Production and Other [Member]
INCOME
Operating Revenues	837,597	611,885	636,528
Operating Expenses:
Operation and Maintenance	173,041	148,856	147,457
Pipeline and Storage and Gathering [Member]
INCOME
Operating Revenues	237,513	206,070	195,819
Operating Expenses:
Operation and Maintenance	123,218	108,640	111,783
Guidance for Hedging [Member] | Cumulative Effect of Adoption of Authoritative Guidance [Member]
EARNINGS REINVESTED IN THE BUSINESS
Balance at Beginning of Year	0	(950)	0
Balance at End of Year		0	(950)
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	0	7,437
Balance at End of Year		0	0
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	0	10,406
Balance at End of Year		$ 0	$ 0