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Derivatives and Fair Value Measurements - Textuals (Details) T in Millions, $ in Millions, $ in Millions | 3 Months Ended | 6 Months Ended |  |  |
--- | --- | --- | --- | --- | ---
Jun. 30, 2020 USD ($) T | Jun. 30, 2019 USD ($) | Jun. 30, 2020 USD ($) T | Jun. 30, 2019 USD ($) | Dec. 31, 2020 T $ / $ | Jun. 30, 2020 AUD ($) T | Dec. 31, 2019 USD ($)
Derivatives, Fair Value [Line Items] |  |  |  |  |  |  |
Transfers between fair value levels 1, 2, and 3 | $ 0.0 | $ 0.0 | $ 0.0 | $ 0.0 |  |  |
Foreign currency option contracts |  |  |  |  |  |  |
Derivatives, Fair Value [Line Items] |  |  |  |  |  |  |
Derivative, Notional Amount |  |  |  |  |  | $ 613.0 |
Coal |  |  |  |  |  |  |
Derivatives, Fair Value [Line Items] |  |  |  |  |  |  |
Derivative, Nonmonetary Notional Amount | T | 1.2 |  | 1.2 |  |  | 1.2 |
Diesel Fuel Hedge Contracts |  |  |  |  |  |  |
Derivatives, Fair Value [Line Items] |  |  |  |  |  |  |
Derivative, Notional Amount |  |  |  |  |  | $ 0.0 |
Scenario, Forecast | Coal |  |  |  |  |  |  |
Derivatives, Fair Value [Line Items] |  |  |  |  |  |  |
Derivative, Nonmonetary Notional Amount | T |  |  |  |  | 0.9 |  |
Scenario, Forecast | Minimum | Foreign currency option contracts |  |  |  |  |  |  |
Derivatives, Fair Value [Line Items] |  |  |  |  |  |  |
Derivative, exchange rate cap | $ / $ |  |  |  |  | 0.70 |  |
Scenario, Forecast | Maximum | Foreign currency option contracts |  |  |  |  |  |  |
Derivatives, Fair Value [Line Items] |  |  |  |  |  |  |
Derivative, exchange rate cap | $ / $ |  |  |  |  | 0.75 |  |
Coal Trading |  |  |  |  |  |  |
Derivatives, Fair Value [Line Items] |  |  |  |  |  |  |
Derivative, initial margin posted | $ 4.5 |  | $ 4.5 |  |  |  | $ 7.9
Derivatives, amount posted in excess of initial margin requirements | 1.7 |  | 1.7 |  |  |  | 1.3
Derivative, variation margin | $ 23.8 |  | $ 23.8 |  |  |  | $ 22.1

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- Definition Amount of right to receive cash collateral under master netting arrangements that have not been offset against derivative liabilities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226016-175313 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 8 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109980867&loc=d3e41678-113959 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (d)(2) -URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312 + Details
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- Definition The net amount as of the balance sheet date of the fair value of derivative assets and derivative liabilities that in accordance with the entity's accounting policy were offset against collateral under a master netting arrangement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 8 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=109980867&loc=d3e41678-113959 + Details
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