Derivative Instruments (Commodity Derivatives) (Details) (USD $)					9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Natural Gas Put Options		Sep. 30, 2013 Natural Gas Put Options Production Period Ending December 31, 2013 MMBTU		Sep. 30, 2013 Natural Gas Put Options Production Period Ending December 31, 2014 MMBTU		Sep. 30, 2013 Natural Gas Put Options Production Period Ending December 31, 2015 MMBTU		Sep. 30, 2013 Natural Gas Put Options Production Period Ending December 31, 2016 MMBTU
Derivative [Line Items]
Volumes (MMBtu)					3,200	[1]	10,500	[1]	8,400	[1]	8,400	[1]
Average Fixed Price (per MMBtu)					3.45	[1]	3.80	[1]	4.00	[1]	4.15	[1]
Fair Value Asset	$ 11,300	$ 16,200	$ 11,300	[2]	$ 100	[2]	$ 3,200	[2]	$ 3,500	[2]	$ 4,500	[2]

[1] “MMBtu” represents million British Thermal Units.

[2] Fair value based on forward New York Mercantile Exchange (“NYMEX”) natural gas prices, as applicable.