Acquisition and Disposition of Properties (Details) (USD $)	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Gas and Oil Acreage [Line Items]
Asset impairment charges	$ 0	$ 21,545,000
Discount rate	10.00%
Expected time period for future natural gas prices curves to shift lower		5 years
Alabama Gas Corporation \| Birmingham Metro Operations Center
Gas and Oil Acreage [Line Items]
Property acreage	11.7
Real Estate, Sales Price	$ 14,000,000
Lease back period after sale	18 months

The charge against earnings resulting from the aggregate write down of all assets from their carrying value to their fair value.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 144

-Paragraph 45, 46, 47

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 28

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: 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=6943989&loc=d3e3602-108585

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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-SubTopic 10

-Section 45

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-URI http://asc.fasb.org/extlink&oid=8077374&loc=d3e2420-110228

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Balance Type:	debit
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