Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)		1 Months Ended		3 Months Ended	9 Months Ended		12 Months Ended
		Apr. 30, 2019	Apr. 30, 2018	Jun. 30, 2019	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Schedule Of Significant Accounting Policies [Line Items]
Cash, cash equivalents, and restricted cash				$ 5,967,000	$ 5,967,000	$ 9,673,000				$ 14,781,000	$ 52,708,000
Cash and cash equivalents				5,717,000	5,717,000					14,531,000
Restricted cash				250,000	250,000					250,000
Captive insurance collateral, debt securities	[1]			57,841,000	57,841,000					45,419,000
Accrued expenses and other current liabilities				145,558,000	145,558,000					116,436,000
Other long-term liabilities				25,382,000	$ 25,382,000					24,012,000
Operating lease expiration year					2033
Undiscounted future minimum lease payments through 2033				$ 125,500,000	$ 125,500,000
ASU 2014-09
Schedule Of Significant Accounting Policies [Line Items]
Revenue, practical expedient, financing component [true false]				true	true
New England Teamsters & Trucking Industry Pension Fund
Schedule Of Significant Accounting Policies [Line Items]
Accrued expenses and other current liabilities				$ 200,000	$ 200,000
Other long-term liabilities				17,000,000	17,000,000
Subsidiaries of Swiss Re
Schedule Of Significant Accounting Policies [Line Items]
Additional payment obligated to pay if degree days exceed ten year average				5,000,000	5,000,000
Payments of derivative hedging contract		$ 2,100,000	$ 1,900,000
Subsidiaries of Swiss Re | Scenario Forecast
Schedule Of Significant Accounting Policies [Line Items]
Derivative maximum payout							$ 5,000,000	$ 5,000,000	$ 5,000,000
Financial Products Corporation
Schedule Of Significant Accounting Policies [Line Items]
Charge on weather hedge contract						$ 1,900,000
Financial Products Corporation | Delivery and branch expenses
Schedule Of Significant Accounting Policies [Line Items]
Charge on weather hedge contract					2,100,000
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				20,400,000	20,400,000
Captive Insurance Collateral | Level 1
Schedule Of Significant Accounting Policies [Line Items]
Captive insurance collateral, debt securities				57,300,000	57,300,000					44,800,000
Captive Insurance Collateral | Mutual Funds
Schedule Of Significant Accounting Policies [Line Items]
Captive insurance collateral, net asset value				$ 500,000	$ 500,000					$ 600,000
Maximum
Schedule Of Significant Accounting Policies [Line Items]
Cash equivalents, highly liquid investments maturity					3 months
Maximum | Subsidiaries of Swiss Re | Scenario Forecast
Schedule Of Significant Accounting Policies [Line Items]
Derivative maximum receivable							$ 12,500,000	$ 12,500,000	$ 12,500,000

[1] See Note 2 – Summary of Significant Accounting Policies – Captive Insurance Collateral.