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Commitments and Contingencies (Details) - Commitments and Agreements (USD $)	3 Months Ended	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2011	Sep. 30, 2010
Long-term Purchase Commitment [Line Items]
Recorded Unconditional Purchase Obligation, Time Period	October 2012
Drilling Plans, Agreement to Secure Drilling Rigs, Number of Agreements		3
Alabama Gas Corporation \| Natural Gas
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Time Period	August 2020
Long-term Purchase Commitment, Minimum Quantity Required	210,454,800
Recorded Unconditional Purchase Obligation	$ 3,700,000	$ 3,700,000
Recorded Unconditional Purchase Obligation, Market Value	3,400,000	3,400,000
Alabama Gas Corporation \| Natural Gas, Delivery and Storage
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	116,000,000
Long-term Purchase Commitment, Time Period	September 2024
Long Term Commitments Expense Recognized in Statements of Operations		36,800,000	38,100,000
Agreement Termination
Long-term Purchase Commitment [Line Items]
Loss Contingency, Range of Possible Loss, Minimum	2,200,000	2,200,000
Loss Contingency, Range of Possible Loss, Maximum	34,000,000	34,000,000
Pending or threatened legal proceedings
Long-term Purchase Commitment [Line Items]
Loss Contingency Accrual, Carrying Value, Period Increase (Decrease)		$ 2,400,000