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Property and Equipment - Summary (Details) - USD ($)
$ in Thousands
Mar. 31, 2019
Dec. 31, 2018
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross $ 164,624 $ 161,133
Less accumulated depreciation (112,613) (109,134)
Total property and equipment, net 52,011 51,999
Construction and transportation equipment    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 148,138 144,630
Buildings and improvements    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 11,139 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 $ 2,627 $ 2,711