Financial Instruments and Risk Management (Financial Instruments and Finance Receivables) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013 counterparty	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Number of Active Counterparties with Whom Company Holds Net Gain Positions	7
Number of Active Counterparties with Whom Company Holds Net Loss Positions	6
Number of Large Counterparties with Whom Company Holds Net Loss Positions	2
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for credit losses, beginning balance	$ 470,000	$ 421,000
Provision	(47,000)	49,000
Allowance for credit losses, ending balance	423,000	470,000
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	1,420,700,000	1,255,800,000
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	1,403,900,000	1,154,000,000
Alabama Gas Corporation
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Recorded Unconditional Purchase Obligation	500,000
Recorded Unconditional Purchase Obligation, Market Value	600,000
Financing Receivable	10,800,000	10,700,000
Financing Receivable, Recorded Investment, Average Balance 0 to 60 Days Past Due	3,000
Average Finance Receivable Term	84 months
Financing Receivable, Recorded Investment, Equal to Greater than 90 Days Past Due	400,000	500,000
Alabama Gas Corporation | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	258,800,000	284,700,000
Alabama Gas Corporation | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	$ 249,900,000	$ 250,000,000