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Property and Equipment (Details) - USD ($)
$ in Thousands
Sep. 30, 2019
Dec. 31, 2018
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross $ 166,442 $ 161,133
Less accumulated depreciation (117,858) (109,134)
Total property and equipment, net 48,584 51,999
Construction and transportation equipment    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 149,859 144,630
Buildings and improvements    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 11,206 11,072
Land    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 2,720 2,720
Office equipment    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross $ 2,657 $ 2,711