Supplementary Information For Oil And Gas Producing Activities (Results Of Operations For Producing Activities) (Details) - USD ($)		12 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Reserve Quantities [Line Items]
Revenues from sales to affiliates		$ 0	$ 0	$ 0
Operating Revenues	[1]	915,668,000	510,291,000	630,126,000
Production/Lifting Costs		267,316,000	203,670,000	186,626,000
Franchise/Ad Valorem Taxes		22,128,000	15,582,000	17,673,000
Purchased Emission Allowance Expense		2,940,000	2,930,000	2,527,000
Accretion Expense		7,743,000	5,237,000	3,723,000
Depreciation, Depletion and Amortization ($0.54, $0.69 and $0.71 per Mcfe of production)		177,055,000	166,759,000	149,881,000
Impairment of Oil and Gas Producing Properties		76,152,000	449,438,000	0
Income Tax Expense		98,593,000	(92,820,000)	64,652,000
Results of Operations for Producing Activities (excluding corporate overheads and interest charges)		263,741,000	(240,505,000)	205,044,000
Depreciation, Depletion and Amortization, per Mcfe of Production		0.54	0.69	0.71
Transfers to Entity's Other Operations		3,061,000	1,921,000	2,532,000
Natural Gas [Member]
Reserve Quantities [Line Items]
Gas (includes transfers to operations of $3,061, $1,921 and $2,532, respectively)	[2]	780,477,000	402,447,000	481,048,000
Oil, Condensate And Other Liquids [Member]
Reserve Quantities [Line Items]
Operating Revenues		$ 135,191,000	$ 107,844,000	$ 149,078,000

[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.