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Fair Value Measurements - Quantative Information about Level 3 Fair Value (Details) - Significant unobservable inputs (Level 3) - Fuel derivatives - Measurement Input, Option Volatility | Sep. 30, 2018
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Minimum | Fourth quarter 2018 |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |
Derivative Asset, Measurement Input | 0.16
Minimum | 2019 |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |
Derivative Asset, Measurement Input | 0.22
Minimum | 2020 |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |
Derivative Asset, Measurement Input | 0.21
Minimum | 2021 |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |
Derivative Asset, Measurement Input | 0.19
Minimum | 2022 |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |
Derivative Asset, Measurement Input | 0.19
Maximum | Fourth quarter 2018 |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |
Derivative Asset, Measurement Input | 0.29
Maximum | 2019 |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |
Derivative Asset, Measurement Input | 0.29
Maximum | 2020 |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |
Derivative Asset, Measurement Input | 0.26
Maximum | 2021 |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |
Derivative Asset, Measurement Input | 0.22
Maximum | 2022 |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |
Derivative Asset, Measurement Input | 0.19

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- Definition Value of input used to measure derivative asset. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb)(2) -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258 + Details
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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. + Details
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