Commitments and Contingencies - Commitments (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013 aircraft aircraft_engine
Commitments and Contingencies Disclosure [Abstract]
Number of spare aircraft engines ordered (in aircraft engine)	2
Number of Aircraft with Extended Leases (in aircraft)	14
Additional Lease Commitments due to Extended Aircraft Leases	$ 72.8
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of Airbus A320 Aircraft Ordered Converted to Airbus A321 Aircraft Ordered (in aircraft)	10
Number of Aircraft with Secured Financing Commitments Scheduled for Delivery (in aircraft)	4
Number of Aircraft without Secured Financing Commitments Scheduled for Delivery (in aircraft)	112
Aircraft and Related Flight Equipment [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Committed expenditures, remainder of 2013	233.0
Committed expenditures, 2014	419.0
Committed expenditures, 2015	834.0
Committed expenditures, 2016	809.0
Committed expenditures, 2017	808.0
Committed expenditures, 2018 and beyond	2,346.0
Reservation System Provider [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Committed expenditures, remainder of 2013	1.9
Committed expenditures, 2014	3.9
Committed expenditures, 2015	3.9
Committed expenditures, 2016	3.9
Committed expenditures, 2017	3.9
Committed expenditures, 2018 and beyond	$ 2.6
Airbus A320 [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of Aircraft Originally Ordered (in aircraft)	96
Number of aircraft ordered (in aircraft)	116
Airbus A321 [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of Additional Aircraft Ordered (in aircraft)	20
Number of aircraft ordered (in aircraft)	30
Airbus A320, current model [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of aircraft ordered (in aircraft)	41
Airbus A320 NEO [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of aircraft ordered (in aircraft)	45
Number of Direct Leased Aircraft Ordered from a Third Party (in aircraft)	5