Commitments and Contingencies (Details)		12 Months Ended
	Feb. 08, 2021 USD ($)	Sep. 30, 2021 USD ($) Bcf	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)
Long Term Purchase Commitment [Line Items]
Self-insured retention		$ 1,000,000
Purchase commitment volume | Bcf		11.9
Purchases under contract		$ 149,400,000	$ 58,500,000	$ 50,800,000
Litigation settlement, expense	$ 1,600,000
Minimum
Long Term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount		1.86
Maximum
Long Term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount		$ 7.03
Supply Commitment
Long Term Purchase Commitment [Line Items]
Contract term		1 year
Supply Commitment | Short-term Contract with Customer
Long Term Purchase Commitment [Line Items]
Purchase commitment volume | Bcf		32.4
Contract term		1 year
Supply Commitment | Long-term Contract with Customer Within Two To Three Years
Long Term Purchase Commitment [Line Items]
Purchase commitment volume | Bcf		12.9
Supply Commitment | Long-term Contract with Customer Within Two To Three Years | Minimum
Long Term Purchase Commitment [Line Items]
Contract term		2 years
Supply Commitment | Long-term Contract with Customer Within Two To Three Years | Maximum
Long Term Purchase Commitment [Line Items]
Contract term		3 years