Derivative Commodity Instruments - Hedging Transactions (Details) (Cash Flow Hedging [Member])	Jun. 30, 2012 Bcf
Natural Gas [Member] | 2012 | NYMEX Swaps [Member]
Derivative [Line Items]
Total Hedged Volumes	6.7
Average Contract Price, per Mcf	4.62
Natural Gas [Member] | 2012 | Basin Specific Swaps - San Juan [Member]
Derivative [Line Items]
Total Hedged Volumes	18.1
Average Contract Price, per Mcf	4.15
Natural Gas [Member] | 2012 | Basin Specific Swaps - Permain [Member]
Derivative [Line Items]
Total Hedged Volumes	3.0
Average Contract Price, per Mcf	2.89
Natural Gas [Member] | 2013 | NYMEX Swaps [Member]
Derivative [Line Items]
Total Hedged Volumes	12.7
Average Contract Price, per Mcf	4.82
Natural Gas [Member] | 2013 | Basin Specific Swaps - San Juan [Member]
Derivative [Line Items]
Total Hedged Volumes	32.8
Average Contract Price, per Mcf	4.56
Natural Gas [Member] | 2013 | Basin Specific Swaps - Permain [Member]
Derivative [Line Items]
Total Hedged Volumes	4.6
Average Contract Price, per Mcf	3.45
Natural Gas [Member] | 2014 | NYMEX Swaps [Member]
Derivative [Line Items]
Total Hedged Volumes	9.1
Average Contract Price, per Mcf	4.65
Natural Gas [Member] | 2014 | Basin Specific Swaps - San Juan [Member]
Derivative [Line Items]
Total Hedged Volumes	25.7
Average Contract Price, per Mcf	4.72
Natural Gas [Member] | 2014 | Basin Specific Swaps - Permain [Member]
Derivative [Line Items]
Total Hedged Volumes	4.6
Average Contract Price, per Mcf	3.79
Crude Oil [Member] | 2012 | NYMEX Swaps [Member]
Derivative [Line Items]
Total Hedged Volumes	3,613
Average Contract Price, per Bbl	88.53
Crude Oil [Member] | 2012 | WTS/WTI Basis Swap [Member]
Derivative [Line Items]
Total Hedged Volumes	1,523
Average Contract Price, per Bbl	(2.95)
Crude Oil [Member] | 2013 | NYMEX Swaps [Member]
Derivative [Line Items]
Total Hedged Volumes	8,098
Average Contract Price, per Bbl	90.65
Crude Oil [Member] | 2013 | WTS/WTI Basis Swap [Member]
Derivative [Line Items]
Total Hedged Volumes	2,768
Average Contract Price, per Bbl	(3.40)
Crude Oil [Member] | 2014 | NYMEX Swaps [Member]
Derivative [Line Items]
Total Hedged Volumes	7,892
Average Contract Price, per Bbl	92.70
Natural Gas Liquids [Member] | 2012 | Liquids Swaps [Member]
Derivative [Line Items]
Total Hedged Volumes	30.0
Average Contract Price, Per Gal	0.98
Natural Gas Liquids [Member] | 2013 | Liquids Swaps [Member]
Derivative [Line Items]
Total Hedged Volumes	44.5
Average Contract Price, Per Gal	1.02
Alabama Gas Corporation [Member] | Natural Gas [Member] | 2012 | NYMEX Swaps [Member]
Derivative [Line Items]
Total Hedged Volumes	7.6
Alabama Gas Corporation [Member] | Natural Gas [Member] | 2013 | NYMEX Swaps [Member]
Derivative [Line Items]
Total Hedged Volumes	1.5