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 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]        
Amount of gain or (loss) recognized in other comprehensive income $ (15,894) $ 131,519 $ 32,682 $ 124,236
Amount reclassified from accumulated other comprehensive income (loss) into fuel expense 6,723 (10,244) 8,508 (19,949)
Fuel contracts | Fuel        
Derivative Instruments, Gain (Loss) [Line Items]        
Amount of gain or (loss) recognized in other comprehensive income 70,508 (4,884) 64,496 (31,087)
Amount reclassified from accumulated other comprehensive income (loss) into fuel expense 7,904 (8,584) 11,429 (16,587)
Foreign currency forward contracts | Depreciation and amortization expense        
Derivative Instruments, Gain (Loss) [Line Items]        
Amount of gain or (loss) recognized in other comprehensive income (88,382) 136,428 (33,889) 155,064
Amount reclassified from accumulated other comprehensive income (loss) into fuel expense (899) (895) (2,058) (1,752)
Interest rate contracts | Interest expense, net        
Derivative Instruments, Gain (Loss) [Line Items]        
Amount of gain or (loss) recognized in other comprehensive income 1,980 (25) 2,075 259
Amount reclassified from accumulated other comprehensive income (loss) into fuel expense $ (282) $ (765) $ (863) $ (1,610)