Derivative Instruments (Location And Amounts Of Derivative Gains And Losses In Condensed Consolidated Statements Of Income) (Details) (USD $) In Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2011		Jun. 30, 2010		Jun. 30, 2011		Jun. 30, 2010
Tax impacts on interest rate swap arrangements	$ 40		$ 13		$ 81		$ (56)
Interest Rate Contracts [Member] | Cash Flow Hedging [Member]
Amount of Gain or (Loss) Recognized in OCI on Derivative (Effective Portion)	69	[1]	21	[1]	139	[2]	(96)	[2]
Commodity Contracts [Member] | Net Realized And Unrealized Gain (Loss) On Fuel Price Derivatives [Member] | Derivatives Not Designated As Hedging Instruments [Member]
Amount of Gain or (Loss) Recognized in Income on Derivative	6,232		9,363		(18,943)		7,583
Financing Interest Expense [Member] | Cash Flow Hedging [Member]
Amount of Gain or (Loss) Reclassified from Accumulated OCI into Income (Effective Portion)	$ (274)		$ (137)		$ (522)		$ (277)

[1] The amount of gain or (loss) recognized in OCI on the Company's interest rate swap arrangements has been recorded net of tax impacts of $40 in 2011 and $13 in 2010.

[2] The amount of gain or (loss) recognized in OCI on the Company's interest rate swap arrangements has been recorded net of tax impacts of $81 in 2011 and $(56) in 2010.