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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

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