Property, Plant and Equipment (Schedule of Property, Plant and Equipment) (Details) - USD ($) $ in Thousands	Jun. 30, 2026	Dec. 31, 2025
Property Plant And Equipment [Line Items]
Total cost of property, plant and equipment	$ 2,524,236	$ 2,951,214
Less accumulated depreciation, depletion, amortization and impairment	1,090,854	1,296,759
Property, plant and equipment, net	1,433,382	1,654,455
Land [Member]
Property Plant And Equipment [Line Items]
Total cost of property, plant and equipment	24,029	29,008
Buildings And Improvements [Member]
Property Plant And Equipment [Line Items]
Total cost of property, plant and equipment	142,762	138,771
Plant, Machinery, Mining Equipment And Transportation Vehicles [Member]
Property Plant And Equipment [Line Items]
Total cost of property, plant and equipment	1,258,397	1,516,095
Mineral Rights And Reserves [Member]
Property Plant And Equipment [Line Items]
Total cost of property, plant and equipment	245,473	370,393
Office And Computer Equipment [Member]
Property Plant And Equipment [Line Items]
Total cost of property, plant and equipment	20,235	20,063
Mine Development [Member]
Property Plant And Equipment [Line Items]
Total cost of property, plant and equipment	674,390	694,779
Asset Retirement Obligation Asset [Member]
Property Plant And Equipment [Line Items]
Total cost of property, plant and equipment	66,689	79,094
Construction In Process [Member]
Property Plant And Equipment [Line Items]
Total cost of property, plant and equipment	$ 92,261	$ 103,011