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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

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