Derivative Commodity Instruments - Hedging Transactions (Details) (Cash Flow Hedging [Member])	Mar. 31, 2012 Bcf
Natural Gas [Member] | 2012 | NYMEX Swaps [Member]
Derivative [Line Items]
Total Hedged Volumes	7.9
Average Contract Price, per Mcf	5.07
Natural Gas [Member] | 2012 | Basin Specific Swaps - San Juan [Member]
Derivative [Line Items]
Total Hedged Volumes	21.1
Average Contract Price, per Mcf	4.60
Natural Gas [Member] | 2013 | NYMEX Swaps [Member]
Derivative [Line Items]
Total Hedged Volumes	11.2
Average Contract Price, per Mcf	4.98
Natural Gas [Member] | 2013 | Basin Specific Swaps - San Juan [Member]
Derivative [Line Items]
Total Hedged Volumes	27.7
Average Contract Price, per Mcf	4.76
Natural Gas [Member] | 2014 | NYMEX Swaps [Member]
Derivative [Line Items]
Total Hedged Volumes	7.8
Average Contract Price, per Mcf	4.76
Natural Gas [Member] | 2014 | Basin Specific Swaps - San Juan [Member]
Derivative [Line Items]
Total Hedged Volumes	22.0
Average Contract Price, per Mcf	4.88
Crude Oil [Member] | 2012 | NYMEX Swaps [Member]
Derivative [Line Items]
Total Hedged Volumes	5,307
Average Contract Price, per Bbl	88.57
Crude Oil [Member] | 2012 | WTS/WTI Basis Swap [Member]
Derivative [Line Items]
Total Hedged Volumes	2,312
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	44.2
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	10.8
Alabama Gas Corporation [Member] | Natural Gas [Member] | 2013 | NYMEX Swaps [Member]
Derivative [Line Items]
Total Hedged Volumes	1.5