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Property, Plant and Equipment, Net - Schedule of Net Property, Plant and Equipment (Detail) - USD ($)
$ in Thousands
Sep. 30, 2019
Dec. 31, 2018
Mar. 15, 2018
Property, Plant and Equipment [Line Items]      
Property, plant and equipment, gross $ 312,079 $ 291,205 $ 15,549
Less: accumulated depreciation and depletion 61,593 42,809  
Total property, plant and equipment, net 250,486 248,396  
Machinery, equipment and tooling      
Property, Plant and Equipment [Line Items]      
Property, plant and equipment, gross 16,863 14,858 1,478
SmartSystems      
Property, Plant and Equipment [Line Items]      
Property, plant and equipment, gross 14,123 5,286  
Vehicles      
Property, Plant and Equipment [Line Items]      
Property, plant and equipment, gross 2,436 1,955  
Furniture and fixtures      
Property, Plant and Equipment [Line Items]      
Property, plant and equipment, gross 1,228 1,140  
Plant and building      
Property, Plant and Equipment [Line Items]      
Property, plant and equipment, gross 160,736 158,882 1,407
Real estate properties      
Property, Plant and Equipment [Line Items]      
Property, plant and equipment, gross 4,913 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 27,683 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 1,883 1,806  
Construction in progress      
Property, Plant and Equipment [Line Items]      
Property, plant and equipment, gross $ 25,022 $ 21,619