Derivative Commodity Instruments - Hedging Transactions (Details) (Cash Flow Hedging)	Mar. 31, 2013 Mcf
Natural Gas | 2013 | NYMEX Swaps
Derivative [Line Items]
Total Hedged Volumes	9,400,000
Average Contract Price, per Mcf	4.83
Natural Gas | 2013 | Basin Specific Swaps - San Juan
Derivative [Line Items]
Total Hedged Volumes	24,400,000
Average Contract Price, per Mcf	4.56
Natural Gas | 2013 | Basin Specific Swaps - Permian
Derivative [Line Items]
Total Hedged Volumes	3,400,000
Average Contract Price, per Mcf	3.45
Natural Gas | 2014 | NYMEX Swaps
Derivative [Line Items]
Total Hedged Volumes	10,600,000
Average Contract Price, per Mcf	4.55
Natural Gas | 2014 | Basin Specific Swaps - San Juan
Derivative [Line Items]
Total Hedged Volumes	25,700,000
Average Contract Price, per Mcf	4.72
Natural Gas | 2014 | Basin Specific Swaps - Permian
Derivative [Line Items]
Total Hedged Volumes	9,700,000
Average Contract Price, per Mcf	3.81
Crude Oil | 2013 | NYMEX Swaps
Derivative [Line Items]
Total Hedged Volumes	6,752,000
Average Contract Price, per Bbl	90.99
Crude Oil | 2013 | WTS/WTI Basis Swaps
Derivative [Line Items]
Total Hedged Volumes	2,701,000	[1]
Average Contract Price, per Bbl	(3.02)	[1]
Crude Oil | 2013 | WTI/WTI Basis Swaps
Derivative [Line Items]
Total Hedged Volumes	2,995,000	[2]
Average Contract Price, per Bbl	(1.00)	[2]
Crude Oil | 2014 | NYMEX Swaps
Derivative [Line Items]
Total Hedged Volumes	9,796,000
Average Contract Price, per Bbl	92.64
Crude Oil | 2015 | NYMEX Swaps
Derivative [Line Items]
Total Hedged Volumes	720,000
Average Contract Price, per Bbl	90.10
Natural Gas Liquids | 2013 | Liquids Swaps
Derivative [Line Items]
Total Hedged Volumes	33,900,000
Average Contract Price, Per Gal	1.02

[1] WTS - West Texas Sour/Midland, WTI - West Texas Intermediate/Cushing

[2] WTI - West Texas Intermediate/Midland, WTI - West Texas Intermediate/Cushing