Supplementary Information For Oil And Gas Producing Activities (Results Of Operations For Producing Activities) (Details) - USD ($)		12 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Reserve Quantities [Line Items]
Revenues from sales to affiliates		$ 0	$ 0	$ 0
Operating Revenues	[1]	510,291,000	630,126,000	558,896,000
Production/Lifting Costs		203,670,000	186,626,000	162,721,000
Franchise/Ad Valorem Taxes		15,582,000	17,673,000	14,355,000
Purchased Emission Allowance Expense		2,930,000	2,527,000	1,883,000
Accretion Expense		5,237,000	3,723,000	4,266,000
Depreciation, Depletion and Amortization ($0.69, $0.71 and $0.67 per Mcfe of production)		166,759,000	149,881,000	119,946,000
Impairment of Oil and Gas Producing Properties		449,438,000	0	0
Income Tax Expense		(92,820,000)	64,652,000	72,723,000
Results of Operations for Producing Activities (excluding corporate overheads and interest charges)		(240,505,000)	205,044,000	183,002,000
Depreciation, Depletion and Amortization, per Mcfe of Production		0.69	0.71	0.67
Transfers to Entity's Other Operations		1,921,000	2,532,000	2,134,000
Natural Gas [Member]
Reserve Quantities [Line Items]
Gas (includes transfers to operations of $1,921, $2,532 and $2,134, respectively)	[2]	402,447,000	481,048,000	390,642,000
Oil, Condensate And Other Liquids [Member]
Reserve Quantities [Line Items]
Operating Revenues		$ 107,844,000	$ 149,078,000	$ 168,254,000

[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.