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Revenue from Contracts with Customers - Revenue By Contract Type (Details) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disaggregation of Revenue [Line Items]                      
Revenues $ 255,175 $ 291,266 $ 268,734 $ 222,492 $ 253,911 $ 304,219 $ 246,412 $ 153,416 $ 1,037,667 $ 957,958 $ 690,123
Heavy Civil Construction                      
Disaggregation of Revenue [Line Items]                      
Revenues                 885,971 849,966 690,123
Heavy Civil Construction | Fixed Unit Price                      
Disaggregation of Revenue [Line Items]                      
Revenues                 733,047 755,840 665,862
Heavy Civil Construction | Lump Sum and Other                      
Disaggregation of Revenue [Line Items]                      
Revenues                 $ 152,924 $ 94,126 $ 24,261