Annual report pursuant to Section 13 and 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
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]      
Amount of Gain (Loss) Recognized in Other Comprehensive Income $ (161,214) $ 304,684 $ 1,711
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Income (Loss) into Income 30,096 (36,795) (95,969)
Designated as Hedging Instrument | Fuel contracts | Fuel      
Derivative Instruments, Gain (Loss) [Line Items]      
Amount of Gain (Loss) Recognized in Other Comprehensive Income (52,949) 50,263 127,470
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Income (Loss) into Income 34,410 (29,721) (88,442)
Designated as Hedging Instrument | Foreign currency contracts | Depreciation and amortization      
Derivative Instruments, Gain (Loss) [Line Items]      
Amount of Gain (Loss) Recognized in Other Comprehensive Income (108,911) 254,070 (124,058)
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Income (Loss) into Income (3,463) (4,077) (3,581)
Designated as Hedging Instrument | Interest rate contracts | Interest expense, net      
Derivative Instruments, Gain (Loss) [Line Items]      
Amount of Gain (Loss) Recognized in Other Comprehensive Income 646 351 (1,701)
Amount of Gain (Loss) Reclassified from Accumulated Other Comprehensive Income (Loss) into Income $ (851) $ (2,997) $ (3,946)