Derivative Commodity Instruments - Hedging Transactions (Details) (Cash Flow Hedging [Member])	Sep. 30, 2012 Bcf
Natural Gas [Member] | 2012 | NYMEX Swaps [Member]
Derivative [Line Items]
Total Hedged Volumes	3.6
Average Contract Price, per Mcf	4.49
Natural Gas [Member] | 2012 | Basin Specific Swaps - San Juan [Member]
Derivative [Line Items]
Total Hedged Volumes	8.9
Average Contract Price, per Mcf	4.14
Natural Gas [Member] | 2012 | Basin Specific Swaps - Permain [Member]
Derivative [Line Items]
Total Hedged Volumes	2.0
Average Contract Price, per Mcf	2.89
Natural Gas [Member] | 2012 | San Juan Basis Swaps [Member]
Derivative [Line Items]
Total Hedged Volumes	0.1
Average Contract Price, per Mcf	(0.23)
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	10.6
Average Contract Price, per Mcf	4.55
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	9.7
Average Contract Price, per Mcf	3.81
Crude Oil [Member] | 2012 | NYMEX Swaps [Member]
Derivative [Line Items]
Total Hedged Volumes	1,850
Average Contract Price, per Bbl	88.51
Crude Oil [Member] | 2012 | WTS/WTI Basis Swap [Member]
Derivative [Line Items]
Total Hedged Volumes	752
Average Contract Price, per Bbl	(2.95)
Crude Oil [Member] | 2013 | NYMEX Swaps [Member]
Derivative [Line Items]
Total Hedged Volumes	8,858
Average Contract Price, per Bbl	90.95
Crude Oil [Member] | 2013 | WTS/WTI Basis Swap [Member]
Derivative [Line Items]
Total Hedged Volumes	3,592
Average Contract Price, per Bbl	(3.03)
Crude Oil [Member] | 2013 | WTI/WTI Basis Swaps [Member]
Derivative [Line Items]
Total Hedged Volumes	1,740
Average Contract Price, per Bbl	(1.13)
Crude Oil [Member] | 2014 | NYMEX Swaps [Member]
Derivative [Line Items]
Total Hedged Volumes	9,796
Average Contract Price, per Bbl	92.64
Natural Gas Liquids [Member] | 2012 | Liquids Swaps [Member]
Derivative [Line Items]
Total Hedged Volumes	15.3
Average Contract Price, Per Gal	0.99
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	4.6
Alabama Gas Corporation [Member] | Natural Gas [Member] | 2013 | NYMEX Swaps [Member]
Derivative [Line Items]
Total Hedged Volumes	1.5