Supplementary Information for Exploration and Production Activities - Results of Operations for Producing Activities (Details)		12 Months Ended
		Sep. 30, 2025 USD ($) uSDollarsPerMCFE	Sep. 30, 2024 USD ($) uSDollarsPerMCFE	Sep. 30, 2023 USD ($) uSDollarsPerMCFE
Reserve Quantities [Line Items]
Operating Revenues	[1]	$ 1,106,120,000	$ 741,076,000	$ 1,038,760,000
Production/Lifting Costs		284,771,000	270,927,000	253,555,000
Franchise/Ad Valorem Taxes		18,267,000	13,468,000	17,532,000
Accretion Expense		7,721,000	5,992,000	5,673,000
Depreciation, Depletion and Amortization ($0.61, $0.69 and $0.63 per Mcfe of production, respectively)		261,712,000	270,648,000	235,694,000
Impairment of Exploration and Production Properties		108,348,000	463,692,000	0
Income Tax Expense (Benefit)		114,502,000	(76,983,000)	145,574,000
Results of Operations for Producing Activities (excluding corporate overheads and interest charges)		310,799,000	(206,668,000)	380,732,000
Revenues from sales to affiliates		0	0	0
Transfers to operations		$ 1,379,000	$ 1,557,000	$ 1,957,000
Depreciation, Depletion and Amortization (per Mcfe of production) | uSDollarsPerMCFE		0.61	0.69	0.63
Gas (includes transfers to operations)
Reserve Quantities [Line Items]
Gas (includes transfers to operations of $1,379, $1,557 and $1,957, respectively)	[2]	$ 1,104,283,000	$ 738,778,000	$ 1,036,499,000
Oil, Condensate and Other Liquids
Reserve Quantities [Line Items]
Operating Revenues		$ 1,837,000	$ 2,298,000	$ 2,261,000

[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.