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Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)
9 Months Ended
Jun. 30, 2023
Jun. 30, 2022
Sep. 30, 2023
Sep. 30, 2022
Sep. 30, 2021
Schedule Of Significant Accounting Policies [Line Items]          
Cash, cash equivalents, and restricted cash $ 57,396,000 $ 9,214,000   $ 14,870,000 $ 5,017,000
Cash and cash equivalents 57,146,000     14,620,000  
Restricted cash 250,000     250,000  
Accrued expenses and other current liabilities 135,267,000     125,561,000  
Other long-term liabilities 16,342,000     14,766,000  
Weather hedge contract receivable 12,500,000        
Interest Rate Swap Agreements | Cash Flow Hedging Derivatives          
Schedule Of Significant Accounting Policies [Line Items]          
Cash flow hedging derivatives, amount 24,000,000        
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 16,000,000.0     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 19,900,000     $ 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