Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis using Significant Unobservable Inputs (Details) (Level 3, Jet fuel options, USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Level 3 | Jet fuel options
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 0	$ 300,000	$ 300,000
Total realized or unrealized gains (losses) included in earnings, net	(4,900,000)	100,000	(200,000)
Purchases	9,700,000	0	0
Sales	0	0	0
Settlements, net	0	400,000	(200,000)
Ending balance	$ 4,800,000	$ 0	$ 300,000