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Property, Plant and Equipment, Net - Schedule of Net Property, Plant and Equipment (Detail) - USD ($)
$ in Thousands
Mar. 31, 2020
Dec. 31, 2019
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross $ 297,709 $ 293,525
Less: accumulated depreciation and depletion 68,501 63,064
Total property, plant and equipment, net 229,208 230,461
Machinery, equipment and tooling    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 20,074 19,683
SmartSystems    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 17,994 15,811
Vehicles    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 2,718 2,419
Furniture and fixtures    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 1,241 1,228
Plant and building    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 170,338 170,283
Real estate properties    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 4,946 4,946
Railroad and sidings    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 27,703 27,701
Land and land improvements    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 21,329 21,320
Asset retirement obligation    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 11,480 11,480
Mineral properties    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 7,442 7,442
Deferred mining costs    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 2,056 2,004
Construction in progress    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross $ 10,388 $ 9,208