Quarterly report pursuant to Section 13 or 15(d)

Significant Accounting Policies (Details)

v3.19.2
Significant Accounting Policies (Details)
$ in Thousands
3 Months Ended 9 Months Ended 12 Months Ended
Apr. 23, 2018
Jun. 30, 2019
USD ($)
Jun. 30, 2018
USD ($)
Jun. 30, 2019
USD ($)
Jun. 30, 2018
USD ($)
Sep. 30, 2018
Concentration Risk [Line Items]            
Revenues   $ 227,290 $ 195,075 $ 545,921 $ 464,395  
Class B Common Stock            
Concentration Risk [Line Items]            
Stock split, conversion ratio 25.2         25.2
Revenues | Customer Concentration Risk | Private            
Concentration Risk [Line Items]            
Revenues   66,207 56,293 166,193 148,525  
Revenues | Customer Concentration Risk | Public            
Concentration Risk [Line Items]            
Revenues   $ 161,083 $ 138,782 $ 379,728 $ 315,870  
Revenues | Department of Transportation | Customer Concentration Risk            
Concentration Risk [Line Items]            
Concentration risk percentage   41.80% 45.60% 39.40% 40.90%  
Revenues | Alabama Department of Transportation | Customer Concentration Risk            
Concentration Risk [Line Items]            
Concentration risk percentage   15.40% 17.00% 12.90% 14.80%  
Revenues | North Carolina Department of Transportation | Customer Concentration Risk            
Concentration Risk [Line Items]            
Concentration risk percentage   13.90% 14.80% 13.40% 13.50%