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Property, Plant and Equipment, Net - Schedule of Net Property, Plant and Equipment (Detail) - USD ($)
$ in Thousands
Jun. 30, 2019
Dec. 31, 2018
Mar. 15, 2018
Property, Plant and Equipment [Line Items]      
Property, plant and equipment, gross $ 305,862 $ 291,205 $ 15,549
Less: accumulated depreciation and depletion 54,884 42,809  
Total property, plant and equipment, net 250,978 248,396  
Machinery, equipment and tooling      
Property, Plant and Equipment [Line Items]      
Property, plant and equipment, gross 16,080 14,858 1,478
SmartSystems      
Property, Plant and Equipment [Line Items]      
Property, plant and equipment, gross 9,532 5,286  
Vehicles      
Property, Plant and Equipment [Line Items]      
Property, plant and equipment, gross 2,214 1,955  
Furniture and fixtures      
Property, Plant and Equipment [Line Items]      
Property, plant and equipment, gross 1,217 1,140  
Plant and building      
Property, Plant and Equipment [Line Items]      
Property, plant and equipment, gross 160,413 158,882 1,407
Real estate properties      
Property, Plant and Equipment [Line Items]      
Property, plant and equipment, gross 4,855 4,601  
Railroad and sidings      
Property, Plant and Equipment [Line Items]      
Property, plant and equipment, gross 27,347 27,347 $ 9,926
Land and land improvements      
Property, Plant and Equipment [Line Items]      
Property, plant and equipment, gross 27,421 27,167  
Asset retirement obligation      
Property, Plant and Equipment [Line Items]      
Property, plant and equipment, gross 19,770 16,469  
Mineral properties      
Property, Plant and Equipment [Line Items]      
Property, plant and equipment, gross 10,075 10,075  
Deferred mining costs      
Property, Plant and Equipment [Line Items]      
Property, plant and equipment, gross 1,806 1,806  
Construction in progress      
Property, Plant and Equipment [Line Items]      
Property, plant and equipment, gross $ 25,132 $ 21,619