Derivatives and Fair Value Measurements - Narrative (Details)	3 Months Ended			6 Months Ended		9 Months Ended
	Sep. 30, 2022 t	Jun. 30, 2022 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2022 USD ($) t	Jun. 30, 2021 USD ($)	Sep. 30, 2022 t	Dec. 31, 2022 USD ($) $ / $	Jun. 30, 2022 AUD ($)	Dec. 31, 2021 USD ($)
Derivatives, Fair Value [Line Items]
Derivative, initial margin posted		$ 544,200,000		$ 544,200,000					$ 130,100,000
Proceeds from common stock issuances, net of costs				222,000,000.0	$ 65,100,000
Net loss (gain) on early debt extinguishment		(2,300,000)	$ (11,800,000)	$ (25,800,000)	15,300,000
Unobservable Measurement Input, Uncertainty, Description				10
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset [Abstract]
Revenue		1,321,900,000	723,400,000	$ 2,013,300,000	1,374,700,000
Fair Value, Inputs, Level 1, 2 and 3
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset [Abstract]
Derivative assets (liabilities), at fair value		0	0	0	0
Trading and Brokerage Coal Deliveries
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset [Abstract]
Revenue			23,200,000		41,100,000
Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Variation margin (received) posted		12,700,000		12,700,000					3,400,000
Unrealized loss recognized in income on derivatives		(31,400,000)	(21,100,000)	(318,300,000)	(33,600,000)
Designated as Hedging Instrument | Net Amount
Derivatives, Fair Value [Line Items]
Variation margin (received) posted		427,400,000		427,400,000					91,800,000
Foreign currency option contracts
Derivatives, Fair Value [Line Items]
Notional amount								$ 758,000,000
Foreign currency option contracts | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Unrealized loss recognized in income on derivatives		(6,300,000)	(1,200,000)	$ (3,000,000.0)	(8,800,000)
Financial trading contracts
Derivatives, Fair Value [Line Items]
Derivative notional amount (in tonnes) | t				1,000,000
Financial trading contracts | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Unrealized loss recognized in income on derivatives		(600,000)	3,800,000	$ 10,200,000	800,000
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 loss recognized in income on derivatives		(24,500,000)	(23,700,000)	(325,500,000)	(25,600,000)
Gain (Loss) on Derivative Instruments | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Unrealized loss recognized in income on derivatives		(40,000,000)		(306,000,000)
Forward Contracts | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Unrealized loss recognized in income on derivatives		(15,000,000)		(20,000,000)
Derivative contracts related to forecasted sales | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Unrealized loss recognized in income on derivatives		(24,500,000)	$ (23,700,000)	(325,500,000)	$ (25,600,000)
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) | $ / $							0.74
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	100,000					900,000
Forecast | Coal Contract to settle in 2022
Derivatives, Fair Value [Line Items]
Derivative notional amount (in tonnes) | t						400,000
Forecast | Coal Contract to settle in 2023
Derivatives, Fair Value [Line Items]
Derivative notional amount (in tonnes) | t						500,000
Coal Trading
Derivatives, Fair Value [Line Items]
Derivative, initial margin posted		$ 116,800,000		$ 116,800,000					$ 38,300,000