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Property, Plant, Equipment and Mine Development
 9 Months Ended
Sep. 30, 2022
Property, Plant and Equipment [Abstract]  
Property, Plant, Equipment and Mine Development Property, Plant, Equipment and Mine Development
The composition of property, plant, equipment and mine development, net, as of September 30, 2022 and December 31, 2021 is set forth in the table below:
September 30, 2022December 31, 2021
(Dollars in millions)
Land and coal interests$2,487.3 $2,494.1 
Buildings and improvements596.1 550.8 
Machinery and equipment1,440.0 1,386.2 
Less: Accumulated depreciation, depletion and amortization(1,705.8)(1,480.5)
Property, plant, equipment and mine development, net$2,817.6 $2,950.6 
Asset Impairment and Other At-Risk Assets
The Company has identified certain assets with an aggregate carrying value of $209.2 million at September 30, 2022 in its Other U.S. Thermal Mining segment whose recoverability is most sensitive to customer demand, customer concentration risk and future economic viability. The Company conducted a review of those assets as of September 30, 2022 and determined that no impairment charges were necessary as of that date.