Accumulated Other Comprehensive Income (Schedule of accumulated other comprehensive income (loss)) (Details) (Commodity Derivatives [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013
Amounts reclassified from accumulated other comprehensive income	$ 0		$ 3,831
Amount of Gain or (Loss) Recognized in Income	0		(1,349)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, before Tax	0		2,482
Tax expense	0		(968)
Total reclassification for the period	0		1,514
Oil And Natural Gas Revenue [Member]
Amounts reclassified from accumulated other comprehensive income	0	[1]	3,831	[1]
Amount of Gain or (Loss) Recognized in Income	0		0
Gain (loss) on derivatives not designated as hedges and hedge ineffectiveness [Member]
Amounts reclassified from accumulated other comprehensive income	0		0
Amount of Gain or (Loss) Recognized in Income	$ 0	[2]	$ (1,349)	[2]

[1] Effective portion of gain (loss).

[2] Ineffective portion of gain (loss).