Financial Instruments - Balance Sheet Location (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
ASSETS
Net Financial Instruments	$ 230,686	$ 80,678
Liabilities
Net Financial Instruments	(5,269)	(2,015)
Designated as Hedging Instrument
ASSETS
Gross / Net Financial Instruments	169,469	73,055
Liabilities
Gross / Net Financial Instruments	0	0
Designated as Hedging Instrument | Deferred Charges And Other Assets | Interest rate agreements
ASSETS
Gross / Net Financial Instruments	169,469	73,055
Designated as Hedging Instrument | Deferred Credits And Other Liabilities | Interest rate agreements
Liabilities
Gross / Net Financial Instruments	0	0
Not Designated as Hedging Instrument
ASSETS
Gross / Net Financial Instruments	61,217	7,623
Liabilities
Gross / Net Financial Instruments	(5,269)	(2,015)
Not Designated as Hedging Instrument | Other Current Assets | Commodity contracts
ASSETS
Gross / Net Financial Instruments	55,073	5,687
Not Designated as Hedging Instrument | Deferred Charges And Other Assets | Commodity contracts
ASSETS
Gross / Net Financial Instruments	6,144	1,936
Not Designated as Hedging Instrument | Other Current Liabilities | Commodity contracts
Liabilities
Gross / Net Financial Instruments	(5,269)	(2,015)
Not Designated as Hedging Instrument | Deferred Credits And Other Liabilities | Commodity contracts
Liabilities
Gross / Net Financial Instruments	$ 0	$ 0