Derivative Instruments (Details)	Mar. 31, 2013 Mcf
Commodity volumes under derivative contracts
Remaining Contractual Volume	10,345,000
Fixed Price Swap
Commodity volumes under derivative contracts
Remaining Contractual Volume	1,650,000
Contract Price	5.16
Price Index	NYMEX	[1]
Fixed Price Swap | Minimum
Commodity volumes under derivative contracts
Term	--01-13
Fixed Price Swap | Maximum
Commodity volumes under derivative contracts
Term	--12-13
Costless Collar Floor
Commodity volumes under derivative contracts
Remaining Contractual Volume	1,650,000
Contract Price	5.00
Price Index	NYMEX	[1]
Costless Collar Floor | Minimum
Commodity volumes under derivative contracts
Term	--01-13
Costless Collar Floor | Maximum
Commodity volumes under derivative contracts
Term	--12-13
Costless Collar Ceiling
Commodity volumes under derivative contracts
Contract Price	5.35
Costless Collar Ceiling | Minimum
Commodity volumes under derivative contracts
Term	--01-13
Costless Collar Ceiling | Maximum
Commodity volumes under derivative contracts
Term	--12-13
Costless Collar Floor
Commodity volumes under derivative contracts
Remaining Contractual Volume	1,620,000
Contract Price	3.25
Price Index	NYMEX	[1]
Costless Collar Floor | Minimum
Commodity volumes under derivative contracts
Term	--01-13
Costless Collar Floor | Maximum
Commodity volumes under derivative contracts
Term	--12-13
Costless Collar Ceiling
Commodity volumes under derivative contracts
Contract Price	4.00
Costless Collar Ceiling | Minimum
Commodity volumes under derivative contracts
Term	--01-13
Costless Collar Ceiling | Maximum
Commodity volumes under derivative contracts
Term	--12-13
Fixed Price Swap
Commodity volumes under derivative contracts
Remaining Contractual Volume	1,825,000
Contract Price	4.27
Price Index	NYMEX	[1]
Fixed Price Swap | Minimum
Commodity volumes under derivative contracts
Term	--01-14
Fixed Price Swap | Maximum
Commodity volumes under derivative contracts
Term	--12-14
Fixed Price Swap
Commodity volumes under derivative contracts
Remaining Contractual Volume	1,800,000
Contract Price	4.20
Price Index	NYMEX	[1]
Fixed Price Swap | Minimum
Commodity volumes under derivative contracts
Term	--01-14
Fixed Price Swap | Maximum
Commodity volumes under derivative contracts
Term	--12-14
Costless Collar Floor
Commodity volumes under derivative contracts
Remaining Contractual Volume	1,800,000
Contract Price	4.00
Price Index	NYMEX	[1]
Costless Collar Floor | Minimum
Commodity volumes under derivative contracts
Term	--01-14
Costless Collar Floor | Maximum
Commodity volumes under derivative contracts
Term	--12-14
Costless Collar Ceiling
Commodity volumes under derivative contracts
Contract Price	4.50
Costless Collar Ceiling | Minimum
Commodity volumes under derivative contracts
Term	--01-14
Costless Collar Ceiling | Maximum
Commodity volumes under derivative contracts
Term	--12-14

[1] New York Mercantile Exchange (“NYMEX”).