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Employee Benefit Plans - Additional Information (Detail)
12 Months Ended 21 Months Ended
Sep. 30, 2023
Sep. 30, 2022
USD ($)
Employee
Program
$ / shares
Sep. 30, 2021
USD ($)
Sep. 30, 2020
USD ($)
Sep. 30, 2015
USD ($)
Sep. 30, 2022
USD ($)
Employee
Program
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 $ 8,200,000 $ 7,900,000    
Multiemployer pension plans, coverage of bargaining agreement, percentage           45.00%
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   125,561,000 121,221,000     $ 125,561,000
Other long-term liabilities   14,766,000 25,244,000     14,766,000
Defined benefit plan funded status included in deferred charges and other assets   3,200,000 $ 4,000,000.0     3,200,000
Net actuarial loss balance in accumulated other comprehensive income to be amortized   11,900,000       11,900,000
Amount to be amortized from accumulated other comprehensive income   $ 1,500       1,500
Discount rate to determine periodic pension expense   5.50% 2.65% 2.45%    
Expected optional pension contribution   $ 0       0
Expected benefit payments for year one   3,900,000       3,900,000
Expected benefit payments for year two   3,900,000       3,900,000
Expected benefit payments for year three   3,900,000       3,900,000
Expected benefit payments for year four   3,900,000       3,900,000
Expected benefit payments for year five   3,900,000       3,900,000
Aggregate expected benefit payment for five years thereafter   $ 16,900,000       $ 16,900,000
Weighted average discount rate   5.50% 2.65% 2.45%   5.50%
Cash and Cash Equivalents            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Pension asset allocation   1.00%       1.00%
Scenario Forecast            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Rate pension plan assets expect to earn 4.60%          
Renewal within Next Fiscal Year            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Multiemployer pension plans, coverage of bargaining agreement, percentage   23.00%        
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   $ 2,055,000 $ 1,833,000 $ 1,654,000    
Management Incentive Compensation Plan            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Partnership incentive distribution   1,028,000 917,000 827,000    
Management Incentive Compensation Plan Executive Officer            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Partnership incentive distribution   $ 434,431 386,857 349,494    
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   $ 500,000 600,000 $ 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   300,000 200,000     $ 300,000
Other long-term liabilities   16,200,000 16,500,000     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   $ 20,200,000 $ 25,800,000     $ 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       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       2
Weighted average discount rate   5.50% 2.65%     5.50%
Domestic Fixed Income            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Pension asset allocation   90.00%       90.00%
Domestic Equities            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Pension asset allocation   7.00%       7.00%
International equity            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Pension asset allocation   2.00%       2.00%