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, 2016
Dec. 31, 2015
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value $ 31,768 $ 3,446
Derivative liabilities, fair value 206,099 344,619
Designated as Hedging Instrument | Fuel Swaps | Prepaid expenses and other assets    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 15,972
Designated as Hedging Instrument | Fuel Swaps | Other long-term assets    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 7,084
Designated as Hedging Instrument | Fuel Swaps | Accrued expenses and other liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liabilities, fair value 82,672 128,740
Designated as Hedging Instrument | Fuel Swaps | Other long-term liabilities    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 7,340  
Derivative liabilities, fair value 79,646 132,494
Designated as Hedging Instrument | Foreign Currency Forward Contracts | Prepaid expenses and other assets    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 6,135
Derivative liabilities, fair value 3,414  
Designated as Hedging Instrument | Foreign Currency Forward Contracts | Other long-term assets    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 2,577 3,446
Derivative liabilities, fair value 386 1,370
Designated as Hedging Instrument | Foreign Currency Forward Contracts | Accrued expenses and other liabilities    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 731  
Derivative liabilities, fair value 13,514 8,737
Designated as Hedging Instrument | Foreign Currency Forward Contracts | Other long-term liabilities    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 1,814 551
Derivative liabilities, fair value 20,165 24,181
Designated as Hedging Instrument | Interest Rate Swap | Accrued expenses and other liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liabilities, fair value 4,328 4,079
Designated as Hedging Instrument | Interest Rate Swap | Other long-term liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liabilities, fair value 3,973 3,395
Not Designated as Hedging Instrument | Fuel Swaps | Accrued expenses and other liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liabilities, fair value 1,801  
Not Designated as Hedging Instrument | Foreign Currency Collar | Accrued expenses and other liabilities    
Derivatives, Fair Value [Line Items]    
Derivative liabilities, fair value $ 42,993