Financial Instruments and Risk Management - Narrative (Details) (USD $) In Millions, unless otherwise specified	8 Months Ended	54 Months Ended	62 Months Ended
	Aug. 31, 2014	Dec. 31, 2013	Aug. 31, 2014	Sep. 30, 2014 gal
Derivative [Line Items]
Federal excise tax	$ 2.1	$ 9.3	$ 11.4
Interest expense, past-due fuel excise tax			$ 0.8
Anticipated jet fuel consumption protected by hedges (in gallons)				32,000,000
Anticipated jet fuel consumption protected by hedges (as a percent)				29.20%
Fuel [Member] | Options Held [Member]
Derivative [Line Items]
Derivative contract, weighted average ceiling price (in USD per gallon)				3.19
Fuel [Member] | Future [Member]
Derivative [Line Items]
Number of derivative contracts		0