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Property, Plant and Equipment, net
 12 Months Ended
Dec. 31, 2024
Property, Plant and Equipment [Abstract]  
Property, Plant and Equipment, net Property, Plant and Equipment, net
Net property, plant and equipment consists of:
 December 31,
 20242023
Machinery, equipment and tooling$43,041 $40,632 
SmartSystems32,551 30,651 
Vehicles3,961 4,082 
Furniture and fixtures1,368 1,466 
Plant and buildings218,546 213,756 
Real estate properties7,161 7,209 
Railroad and sidings35,728 35,491 
Land and land improvements40,627 40,519 
Asset retirement obligation23,283 22,910 
Mineral properties7,442 7,442 
Deferred stripping costs4,434 3,802 
Construction in progress3,216 6,270 
421,358 414,230 
Less: accumulated depreciation and depletion184,666 159,138 
Total property, plant and equipment, net$236,692 $255,092 
Depreciation expense was $27,903, $26,533 and $25,693 for the years ended December 31, 2024, 2023 and 2022, respectively. Depletion expense was $37, $35 and $36 for the years ended December 31, 2024, 2023 and 2022, respectively.
The Company capitalized no interest expense associated with the construction of new property, plant and equipment for the years ended December 31, 2024, 2023 and 2022.