Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	6 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Schedule Of Significant Accounting Policies [Line Items]
Cash, cash equivalents, and restricted cash	$ 22,335,000	$ 17,932,000		$ 14,870,000	$ 5,017,000
Cash and cash equivalents	22,085,000			14,620,000
Restricted cash	250,000			250,000
Accrued expenses and other current liabilities	162,999,000			125,561,000
Other long-term liabilities	15,395,000			14,766,000
Weather hedge contract receivable	12,500,000			0
Interest Rate Swap Agreements | Cash Flow Hedging Derivatives
Schedule Of Significant Accounting Policies [Line Items]
Cash flow hedging derivatives, amount	51,500,000
Propane Assets | Goodwill
Schedule Of Significant Accounting Policies [Line Items]
Assets held-for-sale				2,200,000
Propane Assets | Property and Equipment, Net
Schedule Of Significant Accounting Policies [Line Items]
Assets held-for-sale				800,000
New England Teamsters & Trucking Industry Pension Fund
Schedule Of Significant Accounting Policies [Line Items]
Accrued expenses and other current liabilities	300,000			300,000
Other long-term liabilities	16,100,000			16,200,000
New England Teamsters & Trucking Industry Pension Fund | Significant Other Observable Inputs Level 2
Schedule Of Significant Accounting Policies [Line Items]
Multiemployer plan discounted withdrawal liability	20,600,000			$ 20,200,000
Financial Products Corporation
Schedule Of Significant Accounting Policies [Line Items]
Delivery and branch expense increased (reduced) under weather hedge contract	$ 12,500,000	$ (1,100,000)
Scenario Forecast
Schedule Of Significant Accounting Policies [Line Items]
Derivative maximum payout			$ 5,000,000.0
Maximum
Schedule Of Significant Accounting Policies [Line Items]
Cash equivalents, highly liquid investments maturity	3 months
Derivative maximum receivable	$ 12,500,000