Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Summary Of Significant Accounting Policies [Line Items]
Capitalized Costs Oil And Gas Producing Activities Net		$ 1,874,128	$ 1,758,140
Full cost ceiling test discount factor		10.00%
Impairment of Oil and Gas Producing Properties	$ 76,200	$ 76,152	449,438	$ 0
Amount full cost ceiling exceeds book value of oil and gas properties		842,100
Increase (decrease) estimated future net cash flows		(76,100)	180,000	(17,700)
Depreciation, Depletion and Amortization Expense for Oil and Gas Properties		177,055	166,759	149,881
Goodwill		5,476	5,476
Prior service cost		(700)	(900)
Retained Earnings (Accumulated Deficit)		1,191,175	991,630	$ 1,272,601	$ 1,098,900
Gas stored underground		33,669	33,338
Customer Advances		17,223	15,319
Customer Security Deposits		$ 19,292	$ 17,199
Antidilutive securities		320,222	411,890	242,302
Rate recovery period		1 year
Amount Exceeds LIFO Basis [Member]
Summary Of Significant Accounting Policies [Line Items]
Gas stored underground		$ 74,100
LIFO Method [Member]
Summary Of Significant Accounting Policies [Line Items]
Gas stored underground		33,700
Accumulated Losses [Member]
Summary Of Significant Accounting Policies [Line Items]
Accumulated losses		$ 62,900	$ 89,000
Unamortized Debt Expense [Member]
Summary Of Significant Accounting Policies [Line Items]
Rate recovery period		6 years
Impairment of Oil and Gas Producing Properties [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred Income Tax Benefit	$ 21,000
Guidance for Reclassification of Stranded Tax Effects [Member] | Cumulative Effect of Adoption of Authoritative Guidance [Member]
Summary Of Significant Accounting Policies [Line Items]
Retained Earnings (Accumulated Deficit)			0	$ 0	10,406
Guidance for Recognition and Measurement of Financial Assets and Liabilities [Member] | Cumulative Effect of Adoption of Authoritative Guidance [Member]
Summary Of Significant Accounting Policies [Line Items]
Retained Earnings (Accumulated Deficit)			0	0	7,437
Guidance for Hedging [Member] | Cumulative Effect of Adoption of Authoritative Guidance [Member]
Summary Of Significant Accounting Policies [Line Items]
Increase (Decrease) to Accumulated Other Comprehensive Income				1,000
Retained Earnings (Accumulated Deficit)			$ 0	$ (950)	$ 0