Newly Adopted Accounting Standards and Accounting Standards Not Yet Implemented (Policies)	3 Months Ended
	Mar. 31, 2021
Newly Adopted Accounting Standards and Accounting Standards Not Yet Implemented [Abstract]
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.
Corporate Hedging - Coal Trading	The Company’s risk management function, which is independent of the Company’s coal trading function, is responsible for valuation policies and procedures, with oversight from executive management. The fair value of the Company’s coal derivative assets and liabilities reflects adjustments for credit risk. The Company’s exposure is substantially with electric utilities, energy marketers, steel producers and nonfinancial trading houses.
Fair Value, Assets, Transfers Between Levels	The Company’s policy is to value all transfers between levels using the beginning of period valuation.