Annual report pursuant to Section 13 and 15(d)

Significant Accounting Policies - Concentration of Risks (Details)

v3.24.3
Significant Accounting Policies - Concentration of Risks (Details) - Revenues - Customer Concentration Risk
12 Months Ended
Sep. 30, 2024
Sep. 30, 2023
Sep. 30, 2022
Public      
Concentration Risk [Line Items]      
Concentration risk percentage 63.10% 63.00% 60.90%
Private      
Concentration Risk [Line Items]      
Concentration risk percentage 36.90% 37.00% 39.10%
Departments of Transportation      
Concentration Risk [Line Items]      
Concentration risk percentage 40.70% 36.20% 36.80%
Alabama Department of Transportation      
Concentration Risk [Line Items]      
Concentration risk percentage     10.00%
Florida Department of Transportation      
Concentration Risk [Line Items]      
Concentration risk percentage 13.60% 10.70%  
North Carolina Department of Transportation      
Concentration Risk [Line Items]      
Concentration risk percentage   10.50% 11.20%