Summary of Significant Accounting Policies - Cash Proceeds Received from the Sale of Mileage Credits (Details) (Marketing Component, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Marketing Component
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cash proceeds from sale of miles to non-airline third parties	$ 28,496	$ 24,938	$ 20,954
Portion of proceeds recognized immediately as marketing component	$ 23,124	$ 20,998	$ 16,580