Dispositions of Properties (Details) (Alabama Gas Corporation, USD $)	9 Months Ended	1 Months Ended	3 Months Ended
Sep. 30, 2013	Sep. 30, 2012	Aug. 31, 2013 Birmingham Metro Operations Center	Sep. 30, 2013 Birmingham Metro Operations Center
Gas and Oil Acreage [Line Items]
Gain on disposition of property, plant and equipment	$ (10,889,000)	$ 0	$ 10,900,000
Real Estate, Sales Price				$ 13,800,000
Lease back period after sale				20 months

Amount of gain (loss) on sale or disposal of property, plant and equipment assets, including oil and gas property and timber property.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

Name:	us-gaap_GainLossOnSaleOfPropertyPlantEquipment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration