Quarterly report pursuant to Section 13 or 15(d)

Significant Accounting Policies (Details)

v3.22.4
Significant Accounting Policies (Details) - USD ($)
3 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Sep. 30, 2022
Concentration Risk [Line Items]      
Restricted cash $ 275,000   $ 28,000
Restricted investments 6,737,000   $ 6,866,000
Debt securities, available-for-sale, intent impairments 0 $ 0  
Debt securities, available-for-sale, allowance for credit loss $ 0 $ 0  
Revenues | Customer Concentration Risk | Public      
Concentration Risk [Line Items]      
Concentration risk percentage 61.20% 61.00%  
Revenues | Customer Concentration Risk | Private      
Concentration Risk [Line Items]      
Concentration risk percentage 38.80% 39.00%  
Revenues | Customer Concentration Risk | Department of Transportation      
Concentration Risk [Line Items]      
Concentration risk percentage 33.70% 33.50%  
Revenues | Customer Concentration Risk | Alabama Department of Transportation      
Concentration Risk [Line Items]      
Concentration risk percentage 6.20% 10.10%  
Revenues | Customer Concentration Risk | Florida Department of Transportation      
Concentration Risk [Line Items]      
Concentration risk percentage 8.00% 10.00%  
Revenues | Customer Concentration Risk | North Carolina Department of Transportation      
Concentration Risk [Line Items]      
Concentration risk percentage 10.90% 9.40%