Derivative Instruments (Commodity Derivatives) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012 MMBTU
Derivative [Line Items]
Fair Value Asset/(Liability)	$ 15,100
Natural Gas Put Options [Member]
Derivative [Line Items]
Fair Value Asset/(Liability)	15,100	[1]
Production Period Ending December 31, 2013 [Member] | Natural Gas Put Options [Member]
Derivative [Line Items]
Volumes (mmbtu)	11,800	[2]
Average Fixed Price (per mmbtu)	3.45	[2]
Fair Value Asset/(Liability)	3,000	[1]
Production Period Ending December 31, 2014 [Member] | Natural Gas Put Options [Member]
Derivative [Line Items]
Volumes (mmbtu)	9,800	[2]
Average Fixed Price (per mmbtu)	3.30	[2]
Fair Value Asset/(Liability)	3,700	[1]
Production Period Ending December 31, 2015 [Member] | Natural Gas Put Options [Member]
Derivative [Line Items]
Volumes (mmbtu)	7,800	[2]
Average Fixed Price (per mmbtu)	4.00	[2]
Fair Value Asset/(Liability)	3,700	[1]
Production Period Ending December 31, 2016 [Member] | Natural Gas Put Options [Member]
Derivative [Line Items]
Volumes (mmbtu)	7,800	[2]
Average Fixed Price (per mmbtu)	4.15	[2]
Fair Value Asset/(Liability)	$ 4,700	[1]

[1] Fair value based on forward NYMEX natural gas prices, as applicable.

[2] "MMBtu" represents million British Thermal Units.