Quarterly report pursuant to Section 13 or 15(d)

Significant Accounting Policies - Concentration of Risks (Detail)

v3.19.3.a.u2
Significant Accounting Policies - Concentration of Risks (Detail) - Revenues - Customer Concentration Risk
3 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Department of Transportation    
Concentration Risk [Line Items]    
Concentration risk percentage 3100.00% 3730.00%
Alabama Department of Transportation    
Concentration Risk [Line Items]    
Concentration risk percentage 10.80% 9.60%
North Carolina Department of Transportation    
Concentration Risk [Line Items]    
Concentration risk percentage 8.50% 14.20%