Fair Value Measurements (Details) (Recurring basis, USD $)	Sep. 30, 2011	Dec. 31, 2010
Total
Assets and liabilities subject to fair value measurements
Commodity futures - financial assets	$ 10,158,000	$ 7,052,000
Commodity futures - financial liabilities	8,718,000	12,040,000
Fair value of long-term debt, including current maturities	2,400,000,000	2,500,000,000
Carrying amount of long-term debt, including current maturities	2,400,000,000	2,400,000,000
Significant Other Observable Inputs (Level 2)
Assets and liabilities subject to fair value measurements
Commodity futures - financial assets	10,158,000	7,052,000
Commodity futures - financial liabilities	$ 8,178,000	$ 12,040,000