Other Comprehensive Income and Financial Instruments (Details 1) (USD $)	6 Months Ended
	Jun. 30, 2011 Gallons
Maximum [Member] | Fuel Hedges Contract Five [Member]
Summary of outstanding hedges
Contract Price Per Gallon	$ 4.17
Fuel Hedges Contract Three [Member]
Summary of outstanding hedges
Inception Date	Nov. 05, 2007
Commencement Date	Jan. 05, 2009
Termination Date	Dec. 30, 2013
Notional Amount (in Gallons per Month)	60,000
Contract Price Per Gallon	3.28
Fuel Hedges Contract Four [Member]
Summary of outstanding hedges
Inception Date	Mar. 17, 2008
Commencement Date	Jan. 05, 2009
Termination Date	Dec. 31, 2012
Notional Amount (in Gallons per Month)	50,000
Contract Price Per Gallon	3.72
Fuel Hedges Contract Five [Member]
Summary of outstanding hedges
Inception Date	Mar. 17, 2008
Commencement Date	Jan. 05, 2009
Termination Date	Dec. 31, 2012
Notional Amount (in Gallons per Month)	50,000
Contract Price Per Gallon	3.74
Fuel Hedges Contract Six [Member]
Summary of outstanding hedges
Inception Date	Sep. 22, 2008
Commencement Date	Jan. 01, 2009
Termination Date	Dec. 31, 2011
Notional Amount (in Gallons per Month)	150,000
Contract Price Per Gallon	4.16
Fuel Hedges Contract Eight [Member]
Summary of outstanding hedges
Inception Date	Jul. 10, 2009
Commencement Date	Jan. 01, 2011
Termination Date	Dec. 31, 2011
Notional Amount (in Gallons per Month)	100,000
Contract Price Per Gallon	3.05
Fuel Hedges Contract Nine [Member]
Summary of outstanding hedges
Inception Date	Jul. 10, 2009
Commencement Date	Jan. 01, 2012
Termination Date	Dec. 31, 2012
Notional Amount (in Gallons per Month)	100,000
Contract Price Per Gallon	$ 3.20