Property, Plant and Equipment, net

9 Months Ended

Sep. 30, 2021

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment, net

Property, Plant and Equipment, net

Net property, plant and equipment consisted of:

	September 30, 2021		December 31, 2020
Machinery, equipment and tooling	$	30,456	$	29,002
SmartSystems	27,159		22,352
Vehicles	3,014		2,893
Furniture and fixtures	1,326		1,302
Plant and building	199,958		199,867
Real estate properties	6,496		6,458
Railroad and sidings	27,703		27,703
Land and land improvements	33,155		33,040
Asset retirement obligation	20,730		19,993
Mineral properties	7,442		7,442
Deferred mining costs	2,455		2,123
Construction in progress	6,894		7,489
	366,788		359,664
Less: accumulated depreciation and depletion	103,669		84,988
Total property, plant and equipment, net	$	263,119	$	274,676

Depreciation expense was $6,111 and $5,328 for the three months ended September 30, 2021 and 2020, respectively, and $18,325 and $15,856 for the nine months ended September 30, 2021 and 2020, respectively.