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Employee Benefit Plans - Additional Information (Detail)
12 Months Ended
Sep. 30, 2024
Sep. 30, 2023
USD ($)
Employee
Program
$ / shares
Sep. 30, 2022
USD ($)
Sep. 30, 2021
USD ($)
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   $ 8,500,000 $ 8,500,000 $ 8,200,000  
Multiemployer pension plans, coverage of bargaining agreement, percentage   44.00%      
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   115,606,000 125,561,000    
Other long-term liabilities   16,175,000 14,766,000    
Defined benefit plan funded status included in deferred charges and other assets   2,700,000 $ 3,200    
Net actuarial loss balance in accumulated other comprehensive income to be amortized   $ 10,500,000      
Discount rate to determine periodic pension expense   5.85% 5.50% 2.65%  
Expected optional pension contribution   $ 0      
Expected benefit payments for year four   3,800,000      
Expected benefit payments for year five   3,800,000      
Aggregate expected benefit payment for five years thereafter   $ 16,600,000      
Weighted average discount rate   5.85% 5.50% 2.65%  
Cash and Cash Equivalents          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Pension asset allocation   1.00%      
Scenario Forecast          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Rate pension plan assets expect to earn 5.20%        
Renewal within Next Fiscal Year          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Multiemployer pension plans, coverage of bargaining agreement, percentage   9.00%      
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   0.33333%      
Management And General Partner          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Partnership incentive distribution   $ 2,321,000 $ 2,055,000 $ 1,833,000  
Management Incentive Compensation Plan          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Partnership incentive distribution   1,160,000 1,028,000 917,000  
Management Incentive Compensation Plan Executive Officer          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Partnership incentive distribution   $ 490,485 434,431 386,857  
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 $ 600,000  
New England Teamsters & Trucking Industry Pension Fund          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Multiemployer plan undiscounted withdrawal obligation         $ 48,000,000.0
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    
Other long-term liabilities   16,000,000 16,200,000    
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   $ 18,500,000 $ 20,200,000    
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      
Frozen Defined Benefit Pension Plans          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Number of frozen defined benefit pension plans | Program   2      
Weighted average discount rate     5.50% 2.65%  
Domestic Fixed Income          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Pension asset allocation   90.00%      
Domestic Equities          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Pension asset allocation   7.00%      
International equity          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Pension asset allocation   2.00%