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Summary of Significant Accounting Policies (Details) - USD ($)
 12 Months Ended
Jan. 29, 2021
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Summary of Significant Accounting Policies Textuals        
Corporate Hedging  
From time to time, the Company may utilize various types of derivative instruments to manage its exposure to risks in the normal course of business, including (1) foreign currency exchange rate risk and the variability of cash flows associated with forecasted Australian dollar expenditures made in its Australian mining platform, (2) price risk of fluctuating coal prices related to forecasted sales or purchases of coal, or changes in the fair value of a fixed price physical sales contract, (3) price risk and the variability of cash flows related to forecasted diesel fuel purchased for use in its operations and (4) interest rate risk on long-term debt. These risk management activities are actively monitored for compliance with the Company’s risk management policies.
On a limited basis, the Company engages in the direct and brokered trading of coal and freight-related contracts. Except those contracts for which the Company has elected to apply a normal purchases and normal sales exception, all derivative coal trading contracts are accounted for at fair value. The Company had no diesel fuel or interest rate derivatives in place as of December 31, 2021.
    
Income tax provision   $ 22,800,000 $ 8,000,000.0 $ 46,000,000.0
Accounts receivable, payment term   30 days    
Interest costs capitalized   $ 0 0 0
Royalty Expense   $ 263,000,000 214,700,000 388,600,000
Lease term   10 years    
Minimum annual production of federal coal mining leases on original amount   1.00%    
Monthly federal royalties payable from sale using surface mining methods   12.50%    
Monthly federal royalties payable of production using underground mining methods   8.00%    
Equity method investment   $ 0 0 0
Impairment of investment in equity security   0 0 9,000,000
Restructuring charges for voluntary and involuntary workforce reductions   8,300,000 37,900,000 24,300,000
Restructuring charges   900,000    
Foreign currency remeasurement gain (loss)   (3,100,000) (4,000,000) (2,700,000)
Foreign currency translation adjustment   (1,000,000) 6,100,000 200,000
Asset impairment   0 1,487,400,000 270,200,000
Asset impairment charges related to long-lived assets   $ 0 $ 1,487,400,000 $ 261,200,000
Line of Credit | Letter of Credit        
Summary of Significant Accounting Policies Textuals        
Debt amount incurred $ 324,000,000      
Revolving credit facility, fee on unused borrowings   6.00%    
Commitment fee percentage   0.50%    
Debt covenant, aggregate liquidity at the end of each quarter $ 125,000,000      
Middlemount        
Summary of Significant Accounting Policies Textuals        
Ownership percentage of equity method investment   50.00%    
Minimum | Machinery and equipment        
Summary of Significant Accounting Policies Textuals        
Useful life   1 year    
Maximum | Buildings and improvements        
Summary of Significant Accounting Policies Textuals        
Useful life   29 years    
Maximum | Machinery and equipment        
Summary of Significant Accounting Policies Textuals        
Useful life   15 years