Quarterly report pursuant to Section 13 or 15(d)

Significant Accounting Policies - Concentration of Risks (Detail)

v3.20.2
Significant Accounting Policies - Concentration of Risks (Detail) - Revenues - Customer Concentration Risk
 3 Months Ended 9 Months Ended
Jun. 30, 2020
Jun. 30, 2019
Jun. 30, 2020
Jun. 30, 2019
Department of Transportation        
Concentration Risk [Line Items]        
Concentration risk percentage 36.80% 41.80% 32.30% 39.40%
Alabama Department of Transportation        
Concentration Risk [Line Items]        
Concentration risk percentage 13.20% 15.40% 11.10% 12.90%
North Carolina Department of Transportation        
Concentration Risk [Line Items]        
Concentration risk percentage 9.00% 13.90% 8.40% 13.40%