Derivative Commodity Instruments (Fair Values Of Derivative Instruments In Consolidated Balance Sheets) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Derivative [Line Items]
Total asset derivatives	$ 14,427	$ 2,437
Total liability derivatives	13,694	4,235
Accounts Receivable, Net [Member] | Commodity Forward Contracts [Member]
Derivative [Line Items]
Commodity forward contracts	13,032	0
Derivatives Not Designated as Hedging Instruments, Asset Derivatives	1,395	2,437
Accrued Liabilities [Member] | Commodity Forward Contracts [Member]
Derivative [Line Items]
Derivatives Designated as Hedging Instruments, Liability Derivatives	399	3,262
Derivatives Not Designated as Hedging Instruments, Liability Derivatives	$ 13,295	$ 973