Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended			12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Summary Of Significant Accounting Policies [Line Items]
Capitalized Costs Oil And Gas Producing Activities Net	$ 1,758,140			$ 1,758,140	$ 1,664,553
Full cost ceiling test discount factor	10.00%			10.00%
Impairment of Oil and Gas Producing Properties	$ 253,400	$ 18,200	$ 177,800	$ 449,438	0	$ 0
Increase (decrease) estimated future net cash flows				180,000	(17,700)	(25,100)
Depreciation, Depletion and Amortization Expense for Oil and Gas Properties				166,759	149,881	119,946
Goodwill	5,476			5,476	5,476
Prior service cost	(900)			(900)	(1,000)
Retained Earnings (Accumulated Deficit)	991,630			991,630	1,272,601	$ 1,098,900	$ 851,669
Gas stored underground	33,338			33,338	36,632
Customer Advances	15,319			15,319	13,044
Customer Security Deposits	17,199			$ 17,199	$ 16,210
Antidilutive securities				411,890	242,302	317,899
Amount Exceeds LIFO Basis [Member]
Summary Of Significant Accounting Policies [Line Items]
Gas stored underground	6,600			$ 6,600
LIFO Method [Member]
Summary Of Significant Accounting Policies [Line Items]
Gas stored underground	33,200			33,200
Accumulated Losses [Member]
Summary Of Significant Accounting Policies [Line Items]
Accumulated losses	$ 89,000			$ 89,000	$ 85,800
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				$ 123,100
Guidance for Reclassification of Stranded Tax Effects [Member] | Cumulative Effect of Adoption of Authoritative Guidance [Member]
Summary Of Significant Accounting Policies [Line Items]
Increase (Decrease) to Accumulated Other Comprehensive Income						$ (10,400)
Retained Earnings (Accumulated Deficit)					0	10,406	0
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]
Increase (Decrease) to Accumulated Other Comprehensive Income						(7,400)
Retained Earnings (Accumulated Deficit)					0	7,437	0
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)					$ (950)	$ 0	$ 0