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Property, Plant and Equipment, Net
 12 Months Ended
Dec. 31, 2020
Property, Plant and Equipment, Net [Abstract]  
Property, Plant and Equipment, Net Property, Plant and Equipment, Net
Property, plant and equipment, net includes the following:
 December 31
 20202019
Coal lands and real estate$50,887 $54,647 
Mineral interests14,181 — 
Plant and equipment231,190 190,868 
Property, plant and equipment, at cost296,258 245,515 
Less allowances for depreciation, depletion and amortization123,841 107,454 
 $172,417 $138,061 
Total depreciation, depletion and amortization expense on property, plant and equipment was $15.5 million and $13.6 million during 2020 and 2019, respectively.