Supplementary Information for Exploration and Production Activities - Results of Operations for Producing Activities (Details) - USD ($)		12 Months Ended
		Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Reserve Quantities [Line Items]
Operating Revenues	[1]	$ 741,076,000	$ 1,038,760,000	$ 1,881,680,000
Production/Lifting Costs		270,927,000	253,555,000	283,914,000
Franchise/Ad Valorem Taxes		13,468,000	17,532,000	25,112,000
Purchased Emission Allowance Expense		0	0	1,305,000
Accretion Expense		5,992,000	5,673,000	7,530,000
Depreciation, Depletion and Amortization ($0.69, $0.63 and $0.57 per Mcfe of production, respectively)		270,648,000	235,694,000	202,418,000
Impairment of Exploration and Production Properties		463,692,000	0	0
Income Tax Expense (Benefit)		(76,983,000)	145,574,000	368,925,000
Results of Operations for Producing Activities (excluding corporate overheads and interest charges)		(206,668,000)	380,732,000	992,476,000
Revenues from sales to affiliates		0	0	0
Transfers to operations		1,557,000	1,957,000	5,696,000
Depreciation, Depletion and Amortization (per Mcfe of production)		0.69	0.63	0.57
Gas
Reserve Quantities [Line Items]
Gas (includes transfers to operations of $1,557, $1,957, and $5,696, respectively)	[2]	738,778,000	1,036,499,000	1,730,723,000
Oil, Condensate and Other Liquids
Reserve Quantities [Line Items]
Operating Revenues		$ 2,298,000	$ 2,261,000	$ 150,957,000

[1] Exclusive of hedging gains and losses. See further discussion in Note J — Financial Instruments.

[2] There were no revenues from sales to affiliates for all years presented.