Derivative Instruments (Put And Call Option Contracts) (Details)	6 Months Ended
	Jun. 30, 2011
Fuel price derivative instruments	52,983	[1]
Unleaded Fuel [Member]
Fuel price derivative instruments	36,558	[1]
Diesel [Member]
Fuel price derivative instruments	16,425	[1]

[1] The settlement of the put and call option contracts is based upon the New York Mercantile Exchange's New York Harbor Reformulated Gasoline Blendstock for Oxygen Blending and the U.S. Department of Energy's weekly retail on-highway diesel fuel price for the month.