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				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Amounts reclassified from accumulated other comprehensive income	$ 0		$ (823)		$ 0		$ 3,008
Amount of Gain Recognized in Income	0		1,717		0		368
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax			894				3,376
Tax expense			(350)				(1,318)
Total reclassification for the period			544				2,058
Oil And Natural Gas Revenue [Member]
Amounts reclassified from accumulated other comprehensive income	0	[1]	(823)	[1]	0	[1]	3,008	[1]
Amount of Gain Recognized in Income	0		0		0		0
Gain (loss) on derivatives not designated as hedges and hedge ineffectiveness [Member]
Amounts reclassified from accumulated other comprehensive income	0		0		0		0
Amount of Gain Recognized in Income	$ 0	[2]	$ 1,717	[2]	$ 0	[2]	$ 368	[2]

[1] Effective portion of gain (loss).

[2] Ineffective portion of gain (loss).