Derivative Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Derivative not designated as hedging instrument:
Derivative Assets (Liabilities) not designated as hedging instrument	$ 0		$ 0		$ 311
Derivative not designated as hedging instrument:
Gain (loss) on derivative not designated as hedging instrument	(1,957)	0	(3,384)	(532)
Commodity Contract [Member] | Other Current Assets [Member]
Derivative not designated as hedging instrument:
Derivative Assets (Liabilities) not designated as hedging instrument	0		0		(470)
Commodity Contract [Member] | Sales [Member]
Derivative not designated as hedging instrument:
Gain (loss) on derivative not designated as hedging instrument	(592)	0	(1,498)	(532)
Commodity Contract [Member] | Cost Of Sales [Member]
Derivative not designated as hedging instrument:
Gain (loss) on derivative not designated as hedging instrument	(1,365)	0	(1,886)	0
Cash Collateral [Member] | Other Current Assets [Member]
Derivative not designated as hedging instrument:
Derivative Assets (Liabilities) not designated as hedging instrument	$ 0		$ 0		$ 781