Regulatory Matters (Details) (Alabama Gas Corporation, USD $)	0 Months Ended		1 Months Ended	3 Months Ended		9 Months Ended					3 Months Ended			0 Months Ended
	Dec. 01, 2012	Dec. 01, 2011	Aug. 31, 2013	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 APSC Approved Expension of ESR, November 1, 2010	Sep. 30, 2013 Force Majeure Event Costs APSC Approved Expension of ESR, November 1, 2010	Sep. 30, 2013 Force Majeure Events Costs APSC Approved Expension of ESR, November 1, 2010	Sep. 30, 2013 Environmental Response and Self Insurance Costs APSC Approved Expension of ESR, November 1, 2010	Sep. 30, 2013 Minimum	Sep. 30, 2013 Maximum	Nov. 05, 2013 Subsequent Event	Nov. 05, 2013 Subsequent Event APSC	Nov. 05, 2013 Subsequent Event APSC Minimum	Nov. 05, 2013 Subsequent Event APSC Maximum
Regulatory Matters [Line Items]
Approved return on equity																10.50%	10.95%
Adjusting point															10.80%
Performance based adjustment on adjusting point														0.05%
Equity upon which a return will be permitted														56.50%
Approved increase														1.75%
Allowed return on average common equity												13.15%	13.65%
Rate increases as percentage of prior year revenues													4.00%
Revenue reductions (increase) of rate adjustments	$ (7,800,000)	$ (13,000,000)	$ 10,900,000	$ 4,300,000	$ 1,300,000	$ 10,600,000	$ 6,300,000
Limitation on return on equity as percentage of total capitalization													55.00%
Return on Equity adjustment requirements description						RSE limits the utility’s equity upon which a return is permitted to 55 percent of total capitalization, subject to certain adjustments. Under the inflation-based Cost Control Measurement (CCM) established by the APSC, if the percentage change in operations and maintenance (O&M) expense on an aggregate basis falls within a range of 0.75 points above or below the percentage change in the Consumer Price Index For All Urban Consumers (Index Range), no adjustment is required. If the change in O&M expense on an aggregate basis exceeds the Index Range, three-quarters of the difference is returned to customers. To the extent the change is less than the Index Range, the utility benefits by one-half of the difference through future rate adjustments. The O&M expense base for measurement purposes will be set at the prior year’s actual O&M expense amount unless the Company exceeds the top of the Index Range in two successive years, in which case the base for the following year will be set at the top of the Index Range.
Adjustment requirement threshold for return on equity as percentage of operations and maintenance expenses to Consumer Price Index				0.75
Extraordinary operating and maintenance expenses minimum amount charged to Enhanced Stability Reserve									275,000	412,500	1,000,000
Large commercial and industrial customer budget minimum amount charged to Enhanced Stability Reserve								350,000
Enhanced Stability Reserve refund period				9 years
Enhanced Stability Reserve amortization period				5 years
Enhanced Stability Reserve, amortization expense						$ 660,000