Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements and Derivatives - Derivatives measured at fair value and discloses balance sheet location (Details)

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Fair Value Measurements and Derivatives - Derivatives measured at fair value and discloses balance sheet location (Details) - USD ($)
$ in Thousands
Mar. 31, 2019
Dec. 31, 2018
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value $ 40,751 $ 12,125
Derivative liabilities, fair value 132,146 116,352
Designated as Hedging Instrument    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 38,989 17,217
Derivative liabilities, fair value 137,721 117,879
Derivative Contracts Not Designated as Hedging Instruments    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 3,700 0
Derivative liabilities, fair value 241 0
Fuel contracts | Designated as Hedging Instrument | Prepaid expenses and other assets    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 22,652 2,583
Derivative liabilities, fair value 3,579 1
Fuel contracts | Designated as Hedging Instrument | Other long-term assets    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 12,880 197
Derivative liabilities, fair value 1,996 29
Fuel contracts | Designated as Hedging Instrument | Accrued expenses and other liabilities    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 547 1,173
Derivative liabilities, fair value 2,943 19,547
Fuel contracts | Designated as Hedging Instrument | Other long-term liabilities    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 1,015 933
Derivative liabilities, fair value 10,685 51,184
Fuel contracts | Derivative Contracts Not Designated as Hedging Instruments | Prepaid expenses and other assets    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 3,700 0
Derivative liabilities, fair value 241 0
Foreign currency forward contracts | Designated as Hedging Instrument | Prepaid expenses and other assets    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 1,060 5,285
Derivative liabilities, fair value 0 1,497
Foreign currency forward contracts | Designated as Hedging Instrument | Other long-term assets    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 0 3,514
Derivative liabilities, fair value 0 0
Foreign currency forward contracts | Designated as Hedging Instrument | Accrued expenses and other liabilities    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 376 112
Derivative liabilities, fair value 40,234 5,145
Foreign currency forward contracts | Designated as Hedging Instrument | Other long-term liabilities    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 0 2,874
Derivative liabilities, fair value 77,107 40,476
Interest rate contracts | Designated as Hedging Instrument | Prepaid expenses and other assets    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 459 519
Derivative liabilities, fair value 0 0
Interest rate contracts | Designated as Hedging Instrument | Other long-term assets    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 0 27
Derivative liabilities, fair value 0 0
Interest rate contracts | Designated as Hedging Instrument | Accrued expenses and other liabilities    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 0 0
Derivative liabilities, fair value 624 0
Interest rate contracts | Designated as Hedging Instrument | Other long-term liabilities    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 0 0
Derivative liabilities, fair value 553 0
Total derivatives    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 42,689 17,217
Derivative liabilities, fair value $ 137,962 $ 117,879