Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements and Derivatives - Effects of Derivatives Designated as Cash Flow Hedges (Details 2)

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Fair Value Measurements and Derivatives - Effects of Derivatives Designated as Cash Flow Hedges (Details 2) - Cash Flow Hedging - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]        
Amount of gain or (loss) recognized in other comprehensive income $ 15,365 $ 97,276 $ 48,047 $ 221,512
Amount reclassified from accumulated other comprehensive income (loss) into fuel expense 10,706 (11,644) 19,214 (31,593)
Fuel contracts | Fuel        
Derivative Instruments, Gain (Loss) [Line Items]        
Amount of gain or (loss) recognized in other comprehensive income 24,439 30,452 88,935 (635)
Amount reclassified from accumulated other comprehensive income (loss) into fuel expense 11,595 (9,796) 23,024 (26,383)
Foreign currency forward contracts | Depreciation and amortization expense        
Derivative Instruments, Gain (Loss) [Line Items]        
Amount of gain or (loss) recognized in other comprehensive income (10,062) 66,849 (43,951) 221,913
Amount reclassified from accumulated other comprehensive income (loss) into fuel expense (703) (1,157) (2,761) (2,909)
Interest rate contracts | Interest expense, net        
Derivative Instruments, Gain (Loss) [Line Items]        
Amount of gain or (loss) recognized in other comprehensive income 988 (25) 3,063 234
Amount reclassified from accumulated other comprehensive income (loss) into fuel expense $ (186) $ (691) $ (1,049) $ (2,301)