Quarterly report pursuant to Section 13 or 15(d)

Significant Accounting Policies - Concentration of Risks (Detail)

v3.20.4
Significant Accounting Policies - Concentration of Risks (Detail) - Revenues - Customer Concentration Risk
3 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Department of Transportation    
Concentration Risk [Line Items]    
Concentration risk percentage 27.80% 31.00%
Alabama Department of Transportation    
Concentration Risk [Line Items]    
Concentration risk percentage 7.20% 10.80%