Derivative Instruments (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Loss Recognized in Other Comprehensive Income	$ (78)	$ (2,423)	$ 819	$ (3,431)
Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Loss Recognized in Other Comprehensive Income	(78)	(2,423)	819	(3,431)
Oil and gas sales | Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain Reclassified into Income	$ 436	$ 2,285	$ (18)	$ 8,264