Supplementary Information For Oil And Gas Producing Activities (Results Of Operations For Producing Activities) (Details) - USD ($)		12 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Reserve Quantities [Line Items]
Revenues from sales to affiliates		$ 0	$ 0	$ 0
Operating Revenues	[1]	526,492,000	386,152,000	506,721,000
Production/Lifting Costs		165,991,000	153,914,000	167,800,000
Franchise/Ad Valorem Taxes		15,372,000	13,794,000	20,167,000
Purchased Emission Allowance Expense		1,391,000	700,000	3,089,000
Accretion Expense		4,896,000	6,663,000	6,186,000
Depreciation, Depletion and Amortization ($0.63, $0.85 and $1.49 per Mcfe of production)		108,471,000	136,579,000	234,480,000
Impairment of Oil and Gas Producing Properties		0	948,307,000	1,126,257,000
Income Tax Expense (Benefit)		86,657,000	(368,940,000)	(444,393,000)
Results of Operations for Producing Activities (excluding corporate overheads and interest charges)		143,714,000	(504,865,000)	(606,865,000)
Depreciation, Depletion and Amortization, per Mcfe of Production		0.63	0.85	1.49
Transfers to Entity's Other Operations		2,357,000	1,765,000	1,946,000
Natural Gas [Member]
Reserve Quantities [Line Items]
Natural Gas (includes transfers to operations of $2,357, $1,765 and $1,946, respectively)	[2]	399,975,000	282,619,000	350,673,000
Oil, Condensate And Other Liquids [Member]
Reserve Quantities [Line Items]
Operating Revenues		$ 126,517,000	$ 103,533,000	$ 156,048,000

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

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