Derivative Instruments (Details 2) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Loss Recognized in Other Comprehensive Income	$ (3,454)	$ 860	$ (1,856)	$ (2,558)
Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Loss Recognized in Other Comprehensive Income	(1,471)	(1,982)	3,446	(8,803)
Oil and gas sales | Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain (Loss) Reclassified into Income	$ 4,029	$ (2,842)	$ 6,401	$ (6,245)