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Revenue From Contracts With Customers - Revenue By Contract Type (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Disaggregation of Revenue [Line Items]    
Total Revenue $ 222,492 $ 153,416
Heavy Civil Construction    
Disaggregation of Revenue [Line Items]    
Total Revenue 187,241 153,416
Heavy Civil Construction | Fixed Unit Price    
Disaggregation of Revenue [Line Items]    
Total Revenue 160,236 144,361
Heavy Civil Construction | Lump Sum and Other    
Disaggregation of Revenue [Line Items]    
Total Revenue $ 27,005 $ 9,055