Accumulated Other Comprehensive Income (Loss) (Schedule of accumulated other comprehensive income (loss)) (Details) (Commodity Derivatives [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Other Comprehensive Loss, Derivatives Qualifying as Hedges, before Tax			$ (3,462)				$ (86)
Tax expense			1,337				19
Total reclassification for the period			(2,125)				(67)
Cash Flow Hedging [Member]
Amount of Gain or (Loss) Reclassified from Accumulated OCI into Income	0		(3,210)		0		(202)
Amount of Gain or (Loss) Recognized in Income	0		(252)		0		116
Cash Flow Hedging [Member] | Oil And Natural Gas Revenue [Member]
Amount of Gain or (Loss) Reclassified from Accumulated OCI into Income	0	[1]	(3,210)	[1]	0	[1]	(202)	[1]
Amount of Gain or (Loss) Recognized in Income	0		0		0		0
Cash Flow Hedging [Member] | Gain (loss) on derivatives not designated as hedges and hedge ineffectiveness, net [Member]
Amount of Gain or (Loss) Reclassified from Accumulated OCI into Income	0		0		0		0
Amount of Gain or (Loss) Recognized in Income	$ 0	[2]	$ (252)	[2]	$ 0	[2]	$ 116	[2]

[1] Effective portion of gain (loss).

[2] Ineffective portion of gain (loss).