Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	6 Months Ended		12 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Sep. 30, 2026	Sep. 30, 2024	Sep. 30, 2023
Schedule Of Significant Accounting Policies [Line Items]
Cash, cash equivalents, and restricted cash	$ 18,752,000	$ 12,313,000		$ 117,585,000	$ 45,441,000
Cash and cash equivalents	18,502,000			117,335,000
Restricted cash	250,000			250,000
Derivative maximum payout	5,000,000	0
Accrued expenses and other current liabilities	154,455,000			116,317,000
Other long-term liabilities	16,007,000			16,273,000
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	15,500,000			15,700,000
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	18,500,000			$ 19,300,000
Financial Products Corporation
Schedule Of Significant Accounting Policies [Line Items]
Delivery and branch expense reduced under weather hedge contract	$ 3,100,000	7,500,000
Scenario Forecast
Schedule Of Significant Accounting Policies [Line Items]
Derivative maximum receivable			$ 15,000,000
Derivative maximum payout			$ 5,000,000
Maximum
Schedule Of Significant Accounting Policies [Line Items]
Cash equivalents, highly liquid investments maturity	3 months
Derivative maximum receivable	$ 15,000,000	$ 12,500,000