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, 2015
Dec. 31, 2014
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value $ 4,906  
Derivative liabilities, fair value 257,624 $ 247,577
Designated as Hedging Instrument | Fuel Swaps | Accrued expenses and other liabilities    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 1,744  
Derivative liabilities, fair value 52,407 $ 111,304
Designated as Hedging Instrument | Fuel Swaps | Other long-term liabilities    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value 1,075 190
Derivative liabilities, fair value $ 44,419 $ 77,250
Designated as Hedging Instrument | Foreign Currency Forward Contracts | Accrued expenses and other liabilities    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value    
Derivative liabilities, fair value $ 84,588 $ 29,498
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 $ 11,330 $ 118
Designated as Hedging Instrument | Foreign Currency Forward Contracts | Prepaid expenses and other assets    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value $ 3,077  
Derivative liabilities, fair value    
Designated as Hedging Instrument | Foreign Currency Forward Contracts | Other long-term assets    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value $ 1,730  
Derivative liabilities, fair value    
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 $ 6,100 $ 5,736
Designated as Hedging Instrument | Interest Rate Swap | Other long-term liabilities    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value    
Derivative liabilities, fair value $ 4,114 $ 3,104
Not Designated as Hedging Instrument | Fuel Swaps | Accrued expenses and other liabilities    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value    
Derivative liabilities, fair value $ 18,319  
Not Designated as Hedging Instrument | Foreign Currency Forward Contracts | Prepaid expenses and other assets    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value $ 99  
Derivative liabilities, fair value    
Not Designated as Hedging Instrument | Foreign Currency Collar | Other long-term liabilities    
Derivatives, Fair Value [Line Items]    
Derivative assets, fair value    
Derivative liabilities, fair value $ 36,347 $ 16,744
Not 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   $ 3,823