Summary of Significant Accounting Policies - Maintenance Costs (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Aircraft Maintenance, Materials, and Repairs [Line Items]
Total maintenance expense	$ 60,143	$ 49,460	$ 34,017
Flight hour-based maintenance expense
Aircraft Maintenance, Materials, and Repairs [Line Items]
Total maintenance expense	30,322	25,748	21,974
Non-flight hour-based maintenance expense
Aircraft Maintenance, Materials, and Repairs [Line Items]
Total maintenance expense	$ 29,821	$ 23,712	$ 12,043