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Hedging Activities - Additional Information (Detail) - Fuel Contract | 6 Months Ended
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Jun. 30, 2017 Contract
Derivatives And Hedging Activities [Line Items] |
Fuel hedging contracts outstanding | 0
Cash Flow Hedging | Designated as Hedging Instrument |
Derivatives And Hedging Activities [Line Items] |
Fuel hedges expiration date | 2016-12

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