Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements and Derivatives - Derivatives Measured at Fair Value and Disclosed by Balance Sheet Location (Details)

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Fair Value Measurements and Derivatives - Derivatives Measured at Fair Value and Disclosed by Balance Sheet Location (Details) - USD ($)
$ in Thousands
Jun. 30, 2017
Dec. 31, 2016
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value $ 49,079 $ 20,302
Derivative liabilities, fair value 83,605 238,069
Designated as Hedging Instrument | Fuel Swaps | Prepaid expenses and other assets    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 5,955 20,288
Derivative liabilities, fair value
Designated as Hedging Instrument | Fuel Swaps | Other long-term assets    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 897
Derivative liabilities, fair value
Designated as Hedging Instrument | Fuel Swaps | Accrued expenses and other liabilities    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 1,056
Derivative liabilities, fair value 41,865 41,865
Designated as Hedging Instrument | Fuel Swaps | Other long-term liabilities    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 6,255 13,237
Derivative liabilities, fair value 34,529 38,608
Designated as Hedging Instrument | Foreign Currency Forward Contracts | Prepaid expenses and other assets    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 13,509
Derivative liabilities, fair value 144
Designated as Hedging Instrument | Foreign Currency Forward Contracts | Other long-term assets    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 28,718 14
Derivative liabilities, fair value
Designated as Hedging Instrument | Foreign Currency Forward Contracts | Accrued expenses and other liabilities    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 2,141
Derivative liabilities, fair value 4,665 61,788
Designated as Hedging Instrument | Foreign Currency Forward Contracts | Other long-term liabilities    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value
Derivative liabilities, fair value 88,920
Designated as Hedging Instrument | Interest Rate Swap | Accrued expenses and other liabilities    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value
Derivative liabilities, fair value 2,546 3,331
Designated as Hedging Instrument | Interest Rate Swap | Other long-term liabilities    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value
Derivative liabilities, fair value $ 1,151