Employee Benefit Plans - Additional Information (Detail)			12 Months Ended
	Sep. 30, 2024 USD ($) Employee	Sep. 30, 2023	Sep. 30, 2026	Sep. 30, 2025 USD ($) Program $ / shares	Sep. 30, 2024 USD ($) Employee	Sep. 30, 2023 USD ($)	Sep. 30, 2015 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum participant contribution				60.00%
Partnership aggregate contributions to defined contribution plans				$ 8,900,000	$ 8,500,000	$ 8,500,000
Multiemployer pension plans, coverage of bargaining agreement, percentage				40.00%
Maximum funded for red zone				65.00%
Maximum funded for yellow zone				80.00%
Minimum funded for green zone				80.00%
Partnership contributions in excess of 5% of the plan's total contributions in percentage				5.00%	5.00%	5.00%
Minimum contribution required				$ 0	$ 0	$ 0
Accrued expenses and other current liabilities	$ 116,317,000			119,497,000	116,317,000
Other long-term liabilities	16,273,000			16,171,000	16,273,000
Defined benefit plan funded status included in deferred charges and other assets	$ 2,700,000			2,300,000	$ 2,700,000
Net actuarial loss balance in accumulated other comprehensive income to be amortized				$ 7,700,000
Discount rate to determine periodic pension expense				5.10%	4.70%	5.85%
Expected optional pension contribution				$ 0
Expected benefit payments for year one				3,900,000
Expected benefit payments for year two				3,900,000
Expected benefit payments for year three				3,900,000
Expected benefit payments for year four				3,900,000
Expected benefit payments for year five				3,900,000
Aggregate expected benefit payment for five years thereafter				$ 15,400,000
Weighted average discount rate	4.70%	5.85%		5.10%	4.70%	5.85%
Scenario Forecast
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Rate pension plan assets expect to earn			5.45%
Renewal within Next Fiscal Year
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Multiemployer pension plans, coverage of bargaining agreement, percentage				13.00%
Management
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Incentive distribution percentage of available cash in excess of minimum quarterly distribution				50.00%
Gains interest cash proceeds percentage from the sale of general partner units				50.00%
Employee and Consultant
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Participant's vested percentage of plan benefits				100.00%
Termination of employment or consultation
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Participant's vested percentage of plan benefits				20.00%
Chief executive officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Participant's vested percentage of plan benefits				33.33%
Management And General Partner
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Partnership incentive distribution				$ 2,960,000	$ 2,644,000	$ 2,321,000
Management Incentive Compensation Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Partnership incentive distribution				1,480,000	1,322,000	1,160,000
Management Incentive Compensation Plan Executive Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Partnership incentive distribution				$ 625,733	558,867	490,485
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Participant Contribution				0.00%
Minimum | Management
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Quarterly distribution | $ / shares				$ 0.0675
Other Postretirement Benefit Plan, Defined Benefit
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Partnership aggregate contributions to defined contribution plans				$ 500,000	500,000	$ 500,000
New England Teamsters & Trucking Industry Pension Fund
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Multiemployer plan undiscounted withdrawal obligation							$ 48,000,000
Expected benefit payments in years							30 years
Multiemployer plan annual liability annual payment amount							$ 1,600,000
Accrued expenses and other current liabilities	$ 300,000			300,000	300,000
Other long-term liabilities	15,700,000			15,300,000	15,700,000
New England Teamsters & Trucking Industry Pension Fund | Significant Other Observable Inputs Level 2
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Multiemployer plan discounted withdrawal liability	$ 19,300,000			$ 18,300,000	$ 19,300,000
New England Teamsters & Trucking Industry Pension Fund | Multiemployer Pension Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum funded for red zone				65.00%
New England Teamsters & Trucking Industry Pension Fund | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of employees | Employee	200				200
Frozen Defined Benefit Pension Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of frozen defined benefit pension plans merged | Program				2
Number of frozen defined benefit pension plans | Program				1
Discount rate to determine periodic pension expense	4.70%	5.85%
Domestic Fixed Income
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pension asset allocation				92.00%
Domestic Equities
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pension asset allocation				8.00%