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Derivatives and Fair Value Measurements - Narrative (Details) t in Millions, $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2021 AUD ($) t	Jun. 30, 2021 t	Dec. 31, 2021 $ / $	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Foreign currency option contracts
Derivatives, Fair Value [Line Items]
Notional amount	$ 575,000,000.0
Coal trading contracts
Derivatives, Fair Value [Line Items]
Derivative notional amount (in tonnes) | t	1.5
Diesel Fuel Hedge Contracts
Derivatives, Fair Value [Line Items]
Notional amount	$ 0
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) | $ / $			0.81
Forecast | Coal trading contracts
Derivatives, Fair Value [Line Items]
Derivative notional amount (in tonnes) | t		0.5
Coal Trading
Derivatives, Fair Value [Line Items]
Derivative, initial margin posted				$ 6.5	$ 3.0

X

- Definition

Amount of right to receive cash collateral under master netting arrangements that have not been offset against derivative liabilities.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 13
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

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X

- Definition

Cap rate on a foreign currency derivative for example, but not limited to, a cap or a collar.

+ References

No definition available.

+ Details

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X

- Definition

Floor rate on a foreign currency derivative for example, but not limited to, a floor or a collar.

+ References

No definition available.

+ Details

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X

- Definition

Nominal mass used to calculate payments on a derivative instrument.

+ References

No definition available.

+ Details

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X

- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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