Financial Instruments and Risk Management (Financial Instruments and Finance Receivables) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2011 Fair Value	Dec. 31, 2011 Carrying Value	Dec. 31, 2011 Alabama Gas Corporation	Sep. 30, 2011 Alabama Gas Corporation	Dec. 31, 2010 Alabama Gas Corporation	Dec. 31, 2011 Alabama Gas Corporation Fair Value	Dec. 31, 2011 Alabama Gas Corporation Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value		$ 1,214,900,000	$ 1,155,200,000				$ 274,900,000	$ 250,200,000
Recorded Unconditional Purchase Obligation				3,100,000
Recorded Unconditional Purchase Obligation, Market Value				2,200,000
Financing Receivable				10,500,000		8,800,000
Financing Receivable, Recorded Investment, Average Balance 0 to 60 Days Past Due				3,000
Average Finance Receivable Term					up to 60 months
Financing Receivable, Recorded Investment, Equal to Greater than 90 Days Past Due				432,000
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for credit losses, beginning balance	447,000
Provision	(26,000)
Allowance for credit losses, ending balance	$ 421,000