Property, Plant and Equipment (Schedule of Property, Plant and Equipment) (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Property Plant And Equipment [Line Items]
Property, plant, equipment and equipment, gross	$ 2,148,357	$ 2,145,719
Less accumulated depreciation, depletion and amortization	814,224	748,356
Net property, plant and equipment	1,334,133	1,397,363
Land [Member]
Property Plant And Equipment [Line Items]
Property, plant, equipment and equipment, gross	26,661	27,853
Buildings And Improvements [Member]
Property Plant And Equipment [Line Items]
Property, plant, equipment and equipment, gross	87,926	88,079
Plant, Machinery, Mining Equipment And Transportation Vehicles [Member]
Property Plant And Equipment [Line Items]
Property, plant, equipment and equipment, gross	976,633	963,272
Mineral Rights And Reserves [Member]
Property Plant And Equipment [Line Items]
Property, plant, equipment and equipment, gross	374,326	374,326
Office And Computer Equipment [Member]
Property Plant And Equipment [Line Items]
Property, plant, equipment and equipment, gross	8,953	8,718
Mine Development [Member]
Property Plant And Equipment [Line Items]
Property, plant, equipment and equipment, gross	547,445	566,201
Asset Retirement Obligation Asset [Member]
Property Plant And Equipment [Line Items]
Property, plant, equipment and equipment, gross	67,378	75,215
Construction In Process [Member]
Property Plant And Equipment [Line Items]
Property, plant, equipment and equipment, gross	$ 59,035	$ 42,055