Quarterly report pursuant to Section 13 or 15(d)

Significant Accounting Policies - Additional Information (Details)

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Significant Accounting Policies - Additional Information (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Mar. 31, 2024
Mar. 31, 2023
Mar. 31, 2024
Mar. 31, 2023
Sep. 30, 2023
Concentration Risk [Line Items]          
Restricted cash $ 2,479   $ 2,479   $ 837
Restricted investments $ 15,452   $ 15,452   $ 15,079
Revenues | Customer Concentration Risk | Various Departments of Transportation          
Concentration Risk [Line Items]          
Concentration risk percentage 36.00% 29.80% 36.90% 30.90%  
Revenues | Customer Concentration Risk | Florida Department of Transportation          
Concentration Risk [Line Items]          
Concentration risk percentage 15.80% 11.30% 14.20%    
Private | Revenues | Customer Concentration Risk          
Concentration Risk [Line Items]          
Concentration risk percentage 42.30% 42.10% 41.70% 40.40%  
Public | Revenues | Customer Concentration Risk          
Concentration Risk [Line Items]          
Concentration risk percentage 57.70% 57.90% 58.40% 59.60%