Financial Derivative Instruments (Details) (USD $)	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		1 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Derivatives Not Designated as Hedging Instruments Fuel derivative contracts	Sep. 30, 2012 Derivatives Not Designated as Hedging Instruments Fuel derivative contracts	Sep. 30, 2013 Derivatives Not Designated as Hedging Instruments Fuel derivative contracts	Sep. 30, 2012 Derivatives Not Designated as Hedging Instruments Fuel derivative contracts	Jun. 30, 2013 Derivatives Designated as Hedging Instruments Interest rate derivatives item	Sep. 30, 2013 Derivatives Designated as Hedging Instruments Interest rate derivatives	Sep. 30, 2013 Derivatives Designated as Hedging Instruments Interest rate derivatives	Sep. 30, 2013 Derivatives Designated as Hedging Instruments Foreign currency derivatives	Sep. 30, 2013 Derivatives Designated as Hedging Instruments Foreign currency derivatives
Derivative instrument
Losses realized at settlement					$ (3,790,000)	$ (1,589,000)	$ (11,226,000)	$ (4,318,000)
Reversal of prior period unrealized amounts					4,278,000	3,050,000	5,472,000	2,324,000
Unrealized gains (losses) on contracts that will settle in future periods					2,048,000	5,047,000	(5,177,000)	(501,000)
Gains (losses) on fuel derivatives recorded as nonoperating income (expense)	2,536,000	6,508,000	(10,931,000)	(2,495,000)	2,536,000	6,508,000	(10,931,000)	(2,495,000)
Number of interest rate swap agreements matured									1
Gain recognized in accumulated other comprehensive income (loss) (AOCI)									700,000
Reclass net gains (losses) from AOCI										(200,000)		3,000,000
Accumulated other comprehensive income (loss) expected to be reclassified to earnings in the next 12 months											$ (800,000)		$ 4,000,000
Reclassification estimated time period											12 months		12 months