Derivatives Derivatives (Details 3) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Derivative [Line Items]
Total Assets	$ 61,247	$ (20,480)
Commodity Contract | Purchase contracts
Derivative [Line Items]
Total Assets	45,140
Total Liabilities	(44,734)
Commodity Contract | Sales contracts
Derivative [Line Items]
Total Assets	103,973
Total Liabilities	$ (19,165)