Quarterly report pursuant to Section 13 or 15(d)

Effects of Fuel Options Which Were Not Designated as Hedging Instruments (Detail)

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Effects of Fuel Options Which Were Not Designated as Hedging Instruments (Detail) (Not Designated as Hedging Instrument, Fuel Options, USD $)
In Thousands, unless otherwise specified
 3 Months Ended 9 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
Not Designated as Hedging Instrument | Fuel Options
        
Derivative Instruments, Gain (Loss) [Line Items]        
Gain recognized in other income (expense) $ 430 $ 1,143 $ 1,011 $ 2,858