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Hedging Activities - Additional Information (Detail) - Fuel Contract	6 Months Ended
	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

X

- Definition

Derivative Instrument Expiry Date

+ References

No definition available.

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- Definition

Derivatives And Hedging Activities [Line Items]

+ References

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- Definition

The number of derivative instruments of a particular group held by the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5579245-113959

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- Details

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