Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	1 Months Ended		9 Months Ended		12 Months Ended
	Apr. 30, 2020	Apr. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2021	Sep. 30, 2020	Oct. 01, 2019	Sep. 30, 2019	Sep. 30, 2018
Schedule Of Significant Accounting Policies [Line Items]
Cash, cash equivalents, and restricted cash			$ 66,968,000	$ 5,967,000				$ 5,149,000	$ 14,781,000
Cash and cash equivalents			66,718,000					4,899,000
Restricted cash			250,000					250,000
Captive insurance collateral, debt securities			69,607,000					58,490,000
Additional payment obligated to pay if degree days exceed ten year average			5,000,000.0
Accrued expenses and other current liabilities			153,591,000					120,839,000
Other long-term liabilities			22,235,000					25,746,000
Operating lease right-of-use assets			100,765,000
Current portion of operating lease liabilities			19,391,000
Long-term operating lease liabilities			86,680,000
Interest rate swap
Schedule Of Significant Accounting Policies [Line Items]
Notional Value			65,300,000					45,000,000.0
ASC Topic 842
Schedule Of Significant Accounting Policies [Line Items]
Operating lease right-of-use assets							$ 104,700,000
Current portion of operating lease liabilities							20,100,000
Long-term operating lease liabilities							$ 89,900,000
New England Teamsters & Trucking Industry Pension Fund
Schedule Of Significant Accounting Policies [Line Items]
Accrued expenses and other current liabilities			200,000
Other long-term liabilities			16,800,000
Subsidiaries of Swiss Re
Schedule Of Significant Accounting Policies [Line Items]
Payments and receivables of derivative hedging contract	$ (10,100,000)	$ 2,100,000
Delivery and branch expenses | Financial Products Corporation
Schedule Of Significant Accounting Policies [Line Items]
Change on weather hedge contract			(10,100,000)	$ 2,100,000
Scenario Forecast
Schedule Of Significant Accounting Policies [Line Items]
Derivative maximum payout					$ 5,000,000.0	$ 5,000,000.0
Significant Other Observable Inputs Level 2 | New England Teamsters & Trucking Industry Pension Fund
Schedule Of Significant Accounting Policies [Line Items]
Multiemployer plan discounted withdrawal liability			29,300,000					21,100,000
Captive Insurance Collateral | Level 1
Schedule Of Significant Accounting Policies [Line Items]
Captive insurance collateral, debt securities			68,800,000					58,000,000.0
Captive Insurance Collateral | Mutual Funds
Schedule Of Significant Accounting Policies [Line Items]
Captive insurance collateral, net asset value			$ 800,000					$ 500,000
Maximum
Schedule Of Significant Accounting Policies [Line Items]
Cash equivalents, highly liquid investments maturity			3 months
Maximum | Scenario Forecast
Schedule Of Significant Accounting Policies [Line Items]
Derivative maximum receivable					$ 12,500,000	$ 12,500,000