Derivative Commodity Instruments (Fair Values Of Derivative Instruments In Consolidated Balance Sheets) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Derivative [Line Items]
Total asset derivatives	$ 2,437	$ 47
Total liability derivatives	4,235	46
Accounts Receivable, Net [Member] | Commodity Forward Contracts [Member]
Derivative [Line Items]
Derivatives Not Designated as Hedging Instruments, Asset Derivatives	2,437	47
Accrued Liabilities [Member] | Commodity Forward Contracts [Member]
Derivative [Line Items]
Derivatives Designated as Hedging Instruments, Liability Derivatives	3,262
Derivatives Not Designated as Hedging Instruments, Liability Derivatives	$ 973	$ 46