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Fair Value Measurements - Quantitative Information about Level 3 Fair Value (Details) - Option Model - Implied Volatility - Fuel derivatives | Dec. 31, 2017
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2018 |
Quantitative Information About Level 3 [Line Items] |
Fair Value Measurement Range, Minimum | 11.00%
Fair Value Measurement Range, Maximum | 26.00%
2019 |
Quantitative Information About Level 3 [Line Items] |
Fair Value Measurement Range, Minimum | 17.00%
Fair Value Measurement Range, Maximum | 22.00%
2020 |
Quantitative Information About Level 3 [Line Items] |
Fair Value Measurement Range, Minimum | 17.00%
Fair Value Measurement Range, Maximum | 21.00%
Beyond 2020 |
Quantitative Information About Level 3 [Line Items] |
Fair Value Measurement Range, Minimum | 18.00%
Fair Value Measurement Range, Maximum | 20.00%

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- Definition Minimum range used in level 3 fair value calculation + References No definition available. + Details
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