Derivatives and Fair Value Measurements - Narrative (Details)	3 Months Ended			6 Months Ended
	Jun. 30, 2022 t	Mar. 31, 2022 USD ($) t	Mar. 31, 2021 USD ($)	Jun. 30, 2022 t	Dec. 31, 2022 USD ($) $ / $	Mar. 31, 2022 AUD ($)	Dec. 31, 2021 USD ($)
Derivatives, Fair Value [Line Items]
Derivative, initial margin posted		$ 481,700,000					$ 130,100,000
Proceeds from common stock issuances, net of costs		222,000,000.0	$ 0
Net loss (gain) on early debt extinguishment		$ (23,500,000)	3,500,000
Unobservable Measurement Input, Uncertainty, Description		10
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset [Abstract]
Revenue		$ 691,400,000	651,300,000
Trading and Brokerage Coal Deliveries
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset [Abstract]
Revenue			17,900,000
Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Variation margin (received) posted		13,500,000					3,400,000
Unrealized gain (loss) recognized in income on derivatives		(286,900,000)	(12,500,000)
Designated as Hedging Instrument | Net Amount
Derivatives, Fair Value [Line Items]
Variation margin (received) posted		347,100,000					91,800,000
Foreign currency option contracts
Derivatives, Fair Value [Line Items]
Notional amount						$ 705,000,000
Foreign currency option contracts | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Unrealized gain (loss) recognized in income on derivatives		$ 3,300,000	(7,600,000)
Financial trading contracts
Derivatives, Fair Value [Line Items]
Derivative notional amount (in tonnes) | t		1,600,000
Financial trading contracts | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Unrealized gain (loss) recognized in income on derivatives		$ 10,800,000	(3,100,000)
Diesel Fuel Hedge Contracts
Derivatives, Fair Value [Line Items]
Notional amount						$ 0
Coal Contract and Physical commodity purchase / sale contracts | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Unrealized gain (loss) recognized in income on derivatives		(290,200,000)	(4,900,000)
Gain (Loss) on Derivative Instruments | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Unrealized gain (loss) recognized in income on derivatives		(237,000,000)
Forward Contracts | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Unrealized gain (loss) recognized in income on derivatives		(64,000,000)
Derivative contracts related to forecasted sales | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Unrealized gain (loss) recognized in income on derivatives		(301,000,000.0)	$ (1,800,000)
Forecast
Derivatives, Fair Value [Line Items]
Price per ton					$ 84
Forecast | Foreign currency option contracts
Derivatives, Fair Value [Line Items]
Derivative, exchange rate floor (in dollars per share) | $ / $					0.76
Derivative, exchange rate cap (in dollars per share) | $ / $					0.80
Forecast | Financial trading contracts
Derivatives, Fair Value [Line Items]
Derivative notional amount (in tonnes) | t	300,000			1,300,000
Forecast | Coal Contract to settle in 2022
Derivatives, Fair Value [Line Items]
Derivative notional amount (in tonnes) | t				600,000
Forecast | Coal Contract to settle in 2023
Derivatives, Fair Value [Line Items]
Derivative notional amount (in tonnes) | t				700,000
Coal Trading
Derivatives, Fair Value [Line Items]
Derivative, initial margin posted		$ 134,600,000					$ 38,300,000