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Fair Value Measurements - Quantative Information about Level 3 Fair Value (Details) - Option Model - Implied Volatility - Fuel derivatives | Mar. 31, 2018
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Second quarter 2018 |
Quantitative Information About Level 3 |
Fair Value Measurement Range, Minimum | 14.00%
Fair Value Measurement Range, Maximum | 31.00%
Third quarter 2018 |
Quantitative Information About Level 3 |
Fair Value Measurement Range, Minimum | 21.00%
Fair Value Measurement Range, Maximum | 30.00%
Fourth quarter 2018 |
Quantitative Information About Level 3 |
Fair Value Measurement Range, Minimum | 22.00%
Fair Value Measurement Range, Maximum | 29.00%
2019 |
Quantitative Information About Level 3 |
Fair Value Measurement Range, Minimum | 21.00%
Fair Value Measurement Range, Maximum | 26.00%
2020 |
Quantitative Information About Level 3 |
Fair Value Measurement Range, Minimum | 20.00%
Fair Value Measurement Range, Maximum | 23.00%
2021 |
Quantitative Information About Level 3 |
Fair Value Measurement Range, Minimum | 19.00%
Fair Value Measurement Range, Maximum | 20.00%
2022 |
Quantitative Information About Level 3 |
Fair Value Measurement Range, Minimum | 19.00%
Fair Value Measurement Range, Maximum | 19.00%

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