Derivatives Derivatives by Balance Sheet Location (Details) (USD $)	Dec. 31, 2011	Dec. 31, 2010
Notional Amount of Derivatives, [Abstract]
Notional Amount of Cash Flow Hedge Instruments	$ 164.1
Commodity Contract [Member] | Cash Flow Hedging [Member] | Other Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	97,901,000	27,938,000
Commodity Contract [Member] | Cash Flow Hedging [Member] | Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		529,000
Commodity Contract [Member] | Cash Flow Hedging [Member] | Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		3,191,000
Commodity Contract [Member] | Cash Flow Hedging [Member] | Prepaid Expenses [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	153,376,000	52,022,000
Commodity Contract [Member] | Cash Flow Hedging [Member] | Assets, Total [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	251,277,000	79,960,000
Commodity Contract [Member] | Cash Flow Hedging [Member] | Liabilities, Total [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		$ 3,720,000