Financial Instruments (Details 4) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Schedule of Realized and Unrealized Gains (Losses) from Commodity Derivatives
Realized and unrealized gains (losses) from commodity derivatives	$ (631)	$ 2,960	$ (342)	$ 62