Derivative Instruments (Details) (Forward Contracts [Member], USD $)	Jun. 30, 2012 gal
Sales [Member]
Outstanding trading contracts
Quantity in Gallons	5,754,000
Weighted Average Contract Prices	$ 0.8933
Sales [Member] | Maximum [Member]
Outstanding trading contracts
Estimated Market Prices	$ 1.3775
Sales [Member] | Minimum [Member]
Outstanding trading contracts
Estimated Market Prices	$ 0.7200
Purchase [Member]
Outstanding trading contracts
Quantity in Gallons	5,670,000
Weighted Average Contract Prices	$ 0.8724
Purchase [Member] | Maximum [Member]
Outstanding trading contracts
Estimated Market Prices	$ 1.3300
Purchase [Member] | Minimum [Member]
Outstanding trading contracts
Estimated Market Prices	$ 0.6825