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Property, Plant and Equipment, net
 12 Months Ended
Dec. 31, 2023
Property, Plant and Equipment [Abstract]  
Property, Plant and Equipment, net Property, Plant and Equipment, net
Net property, plant and equipment consists of:
 December 31,
 20232022
Machinery, equipment and tooling$40,632 $36,483 
SmartSystems30,651 28,376 
Vehicles4,082 3,835 
Furniture and fixtures1,466 1,421 
Plant and buildings213,756 200,480 
Real estate properties7,209 6,155 
Railroad and sidings35,491 33,698 
Land and land improvements40,519 40,433 
Asset retirement obligation22,910 22,583 
Mineral properties7,442 7,442 
Deferred stripping costs3,802 2,470 
Construction in progress6,270 10,421 
414,230 393,797 
Less: accumulated depreciation and depletion159,138 134,954 
Total property, plant and equipment, net$255,092 $258,843 
Depreciation expense was $26,533, $25,693 and $24,667 for the years ended December 31, 2023, 2022 and 2021, respectively. Depletion expense was $35, $36 and $36 for the years ended December 31, 2023, 2022 and 2021, respectively.
The Company capitalized no interest expense associated with the construction of new property, plant and equipment for the years ended December 31, 2023, 2022 and 2021.