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Revenue from Customers Revenue from Customers - Backlog By Segment (Details) - USD ($)
$ in Thousands
Dec. 31, 2020
Dec. 31, 2019
Segment Reporting Information [Line Items]    
Backlog $ 1,175,388 $ 1,068,025
Heavy Civil Construction    
Segment Reporting Information [Line Items]    
Backlog 898,183 834,049
Specialty Service    
Segment Reporting Information [Line Items]    
Backlog $ 277,205 $ 233,976