Commitments and Contingencies (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Jun. 30, 2012	Dec. 31, 2012 aircraft_engine
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of spare aircraft engines ordered		3
Cash payment including interest to pre-IPO stockholders pursuant to tax receivable agreement	$ 27.2
Interest included in cash payment to pre-IPO stockholders pursuant to tax receivable agreement	0.3
Aircraft and Related Flight Equipment
Unrecorded Unconditional Purchase Obligation [Line Items]
Committed expenditures, 2013		323.0
Committed expenditures, 2014		354.0
Committed expenditures, 2015		523.0
Committed expenditures, 2016		505.0
Committed expenditures, 2017		613.0
Committed expenditures, 2018 and beyond		2,339.0
Reservation System Provider
Unrecorded Unconditional Purchase Obligation [Line Items]
Committed expenditures, 2013		3.1
Committed expenditures, 2014		3.7
Committed expenditures, 2015		3.7
Committed expenditures, 2016		3.7
Committed expenditures, 2017		3.7
Committed expenditures, 2018 and beyond		2.5
Airbus A320
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of aircraft ordered (in aircraft)		106
Airbus used A319 aircraft
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of aircraft ordered (in aircraft)		2
Airbus A320 current model
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of aircraft ordered (in aircraft)		54
Airbus A320 Neo
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of aircraft ordered (in aircraft)		50