Commitments and Contingencies - Fixed Maintenance Reserve Payments (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013
Commitments and Contingencies Disclosure [Abstract]
Fixed maintenance reserve payments, future estimated payments due, the remainder of 2013	$ 5.1
Fixed maintenance reserve payments, future estimated payments due, 2014	10.6
Fixed maintenance reserve payments, future estimated payments due, 2015	11.0
Fixed maintenance reserve payments, future estimated payments due, 2016	11.4
Fixed maintenance reserve payments, future estimated payments due, 2017	11.1
Fixed maintenance reserve payments, future estimated payments due, 2018 and beyond	$ 40.0

Fixed Maintenance Reserve Payments, Future Estimated Payments Due, Due After Five Years

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Fixed Maintenance Reserve Payments, Future Estimated Payments Due, Due Within Five Years

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Fixed Maintenance Reserve Payments, Future Estimated Payments Due, Due Within Four Years

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Fixed Maintenance Reserve Payments, Future Estimated Payments Due, Due Within Three Years

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Fixed Maintenance Reserve Payments, Future Estimated Payments Due, Due Within Two Years

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Fixed Maintenance Reserve Payments, Future Estimated Payments Due, Within Current Fiscal Year

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