Quarterly report pursuant to Section 13 or 15(d)

Significant Accounting Policies (Detail)

v3.10.0.1
Significant Accounting Policies (Detail)
3 Months Ended
Apr. 23, 2018
Dec. 31, 2018
Dec. 31, 2017
Class B Common Stock      
Concentration Risk [Line Items]      
Stock split, conversion ratio 25.2    
Revenues | Customer Concentration Risk | Department of Transportation      
Concentration Risk [Line Items]      
Concentration risk percentage   37.30% 37.30%
Revenues | Customer Concentration Risk | Alabama Department of Transportation      
Concentration Risk [Line Items]      
Concentration risk percentage   9.60% 13.20%
Revenues | Customer Concentration Risk | North Carolina Department of Transportation      
Concentration Risk [Line Items]      
Concentration risk percentage   14.20% 13.20%