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Fuel Risk Management (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Fuel Risk Management      
Quantity of jet fuel covered by outstanding derivative contracts (in gallons) 127,000,000    
Settlement period of derivative contracts 18 months    
Derivatives Not Designated as Hedging Instruments | Fuel derivative contracts
     
Mark to fair value gains (losses) on undesignated fuel hedges:      
Losses realized at settlement $ (7,372) $ (430) $ (3,199)
Reversal of prior period unrealized amounts 2,367 (3,920) (226)
Unrealized gains (losses) on contracts that will settle in future periods (6,325) (2,512) 4,066
Gains (losses) on fuel derivatives recorded as nonoperating income (expense) $ (11,330) $ (6,862) $ 641