Long-Term Debt and Bank Facility Borrowings - Additional Information (Detail) - USD ($)			3 Months Ended	6 Months Ended		12 Months Ended
		Dec. 04, 2019	Mar. 31, 2022	Mar. 31, 2022	Mar. 31, 2021	Sep. 30, 2022	Sep. 30, 2021
Debt Instrument [Line Items]
Additional term loan repayments				$ 11,365,000	$ 6,500,000
Hedging positions and payable amounts secured under credit facility			$ 0	0			$ 0
Letters of credit issued and outstanding			5,100,000	5,100,000			3,100,000
Long-term debt, fair value	[1]		284,858,000	284,858,000			119,118,000
Revolving credit facility outstanding			185,723,000	185,723,000			8,618,000
Availability under credit agreement			$ 146,700,000	$ 146,700,000			$ 171,500,000
Term Loan
Debt Instrument [Line Items]
Debt instrument, effective interest rate			4.30%	4.30%			4.30%
Long-term debt, fair value	[1],[2]		$ 99,135,000	$ 99,135,000			$ 110,500,000
Revolving Credit Facility
Debt Instrument [Line Items]
Debt instrument, effective interest rate			2.30%	2.30%			2.50%
Revolving credit facility outstanding			$ 185,700,000	$ 185,700,000			$ 8,600,000
Credit Agreement
Debt Instrument [Line Items]
Non Seasonal maximum borrowing capacity under revolving credit facility		$ 300,000,000	400,000,000	$ 400,000,000
Maximum borrowing capacity (heating season December to April) under revolving credit facility		450,000,000
Issuance of line of credit for working capital purposes		$ 25,000,000
Senior secured term loan maturity date		Dec. 04, 2024
Increase in revolving credit facility			100,000,000
Facility size that can be increased additional without consulting bank group			200,000,000
Facility size that can be increased without consulting bank group			$ 200,000,000
Term loan annual payment percentage		25.00%
Commitment fee on the unused portion of the facility from December through April		0.30%
Commitment fee on the unused portion of the facility from May through November		0.20%
Minimum fixed charge coverage ratio		110.00%
Availability percentage to maximum facility size		12.50%
Credit Agreement | Scenario Forecast
Debt Instrument [Line Items]
Additional term loan repayments						$ 4,900,000
Credit Agreement | Maximum
Debt Instrument [Line Items]
Senior secured leverage ratio during quarters ending June or September		300.00%
Senior secured leverage ratio during quarters ending December or March		450.00%
Credit Agreement | Quarterly
Debt Instrument [Line Items]
Term loan periodic payment		$ 3,250,000
Credit Agreement | Annually | Maximum
Debt Instrument [Line Items]
Term loan periodic payment		12,000,000
Credit Agreement | Term Loan
Debt Instrument [Line Items]
Outstanding term loan		$ 130,000,000
Senior secured term loan maturity period		5 years

[1] The face amount of the Company’s variable rate long-term debt approximates fair value.

[2] Carrying amounts are net of unamortized debt issuance costs of $0.4 million as of March 31, 2022 and $0.5 million as of September 30, 2021.