Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended		12 Months Ended
	Apr. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	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		$ 14,792,000	$ 24,039,000				$ 5,149,000	$ 14,781,000
Cash and cash equivalents		14,542,000					4,899,000
Restricted cash		250,000					250,000
Captive insurance collateral, debt securities		62,703,000					58,490,000
Additional payment obligated to pay if degree days exceed ten year average		5,000,000
Accrued expenses and other current liabilities		132,837,000					120,839,000
Other long-term liabilities		20,838,000					25,746,000
Operating lease right-of-use assets		103,492,000
Current portion of operating lease liabilities		20,202,000
Long-term operating lease liabilities		88,707,000
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		16,900,000
Financial Products Corporation
Schedule Of Significant Accounting Policies [Line Items]
Charge on weather hedge contract			$ 2,000,000
Subsidiaries of Swiss Re
Schedule Of Significant Accounting Policies [Line Items]
Payments of derivative hedging contract	$ 2,100,000
Delivery and branch expenses | Financial Products Corporation
Schedule Of Significant Accounting Policies [Line Items]
Charge on weather hedge contract		3,000,000
Scenario Forecast
Schedule Of Significant Accounting Policies [Line Items]
Derivative maximum payout				$ 5,000,000	$ 5,000,000
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		22,100,000
Captive Insurance Collateral | Level 1
Schedule Of Significant Accounting Policies [Line Items]
Captive insurance collateral, debt securities		61,200,000					58,000,000
Captive Insurance Collateral | Mutual Funds
Schedule Of Significant Accounting Policies [Line Items]
Captive insurance collateral, net asset value		$ 1,500,000					$ 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