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Fair Value Measurements and Derivative Instruments - Derivatives Not Designated as Hedging Instruments (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Derivative Instruments    
Amount of gain (loss) recognized in income on derivatives $ 4,780 $ 7,810
Foreign currency forward contracts | Other income (expense)    
Derivative Instruments    
Amount of gain (loss) recognized in income on derivatives 5,014 5,635
Fuel swaps | Other income (expense)    
Derivative Instruments    
Amount of gain (loss) recognized in income on derivatives (98) 2,205
Fuel swaps | Fuel cost    
Derivative Instruments    
Amount of gain (loss) recognized in income on derivatives $ (136) $ (30)