Commitments and Contingencies (Details) $ in Millions		12 Months Ended
	Mar. 29, 2018 USD ($)	Sep. 30, 2018 USD ($) Bcf	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
Long Term Purchase Commitment [Line Items]
Self-insured retention		$ 1.0
Purchases under contract		$ 57.2	$ 49.7	$ 85.3
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]
Contract term		1 year
Purchase commitment volume | Bcf		54,100
Supply Commitment | Long-term Contract with Customer Within Two To Three Years
Long Term Purchase Commitment [Line Items]
Purchase commitment volume | Bcf		37,200
Minimum | Supply Commitment | Long-term Contract with Customer Within Two To Three Years
Long Term Purchase Commitment [Line Items]
Contract term		2 years
Maximum | Supply Commitment | Long-term Contract with Customer Within Two To Three Years
Long Term Purchase Commitment [Line Items]
Contract term		3 years
Civil Action Dallas Texas
Long Term Purchase Commitment [Line Items]
Damages sought	$ 1.0