Quarterly report pursuant to Section 13 or 15(d)

Effects of Derivatives Designated as Cash Flow Hedges (Detail)

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Effects of Derivatives Designated as Cash Flow Hedges (Detail) (Cash Flow Hedge, Fuel Swaps, USD $)
In Thousands, unless otherwise specified
3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Cash Flow Hedge | Fuel Swaps
   
Fair Value, Option, Quantitative Disclosures [Line Items]    
Gain recognized in other comprehensive income (loss) - effective portion $ 4,706 $ 26,464
Gain recognized in other income (expense) - ineffective portion 221 1,244
Amount reclassified from accumulated other comprehensive income (loss) into fuel expense $ (2,263) $ (9,239)