Derivative Commodity Instruments (Fair Values Of Derivative Instruments In Consolidated Balance Sheets) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Derivative [Line Items]
Derivatives designated as hedging instruments, Asset Derivatives	$ (5,729)	$ 3,262
Total asset derivatives	7,171	2,437
Total liability derivatives	939	4,235
Accounts Receivable, Net [Member] | Commodity Forward Contracts [Member]
Derivative [Line Items]
Derivatives designated as hedging instruments, Asset Derivatives	5,729
Derivatives not designated as hedging instruments, Asset Derivatives	1,442	2,437
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	$ 939	$ 973