Commitments and Contingencies (Details) - Commitments and Agreements (USD $) In Millions, unless otherwise specified	9 Months Ended
Sep. 30, 2012 agreements
Long-term Purchase Commitment [Line Items]
Drilling Plans, Agreement to Secure Drilling Rigs, Number of Agreements	3
Agreement Termination
Long-term Purchase Commitment [Line Items]
Loss Contingency, Range of Possible Loss, Maximum	24
Pending or threatened legal proceedings
Long-term Purchase Commitment [Line Items]
Loss Contingency Accrual, Carrying Value, Period Increase (Decrease)	1.4
Alabama Gas Corporation
Long-term Purchase Commitment [Line Items]
Chain of Title, Manufactured Gas Plant Sites	9
Chain of Title, Manufactured Gas Distribution Sites	5
Crude Oil [Member]
Long-term Purchase Commitment [Line Items]
Oil and Gas Delivery Commitments and Contracts, Remaining Contractual Volume	33.4
Natural Gas \| Alabama Gas Corporation
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Time Period	August 2020
Long-term Purchase Commitment, Minimum Quantity Required	177
Recorded Unconditional Purchase Obligation, Time Period	March 2013
Recorded Unconditional Purchase Obligation	0.8
Recorded Unconditional Purchase Obligation, Market Value	0.8
Natural Gas, Delivery and Storage \| Alabama Gas Corporation
Long-term Purchase Commitment [Line Items]
Long-term Purchase Commitment, Amount	74
Long-term Purchase Commitment, Time Period	September 2024
Long Term Commitments Expense Recognized in Statements of Operations	36.8
Wholly Owned Properties [Member] \| Alabama Gas Corporation
Long-term Purchase Commitment [Line Items]
Chain of Title, Manufactured Gas Plant Sites	4
Chain of Title, Manufactured Gas Distribution Sites	1

Chain of Title, Manufactured Gas Distribution Sites

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- Definition

Chain of Title, Manufactured Gas Plant Sites

+ References

No definition available.

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- Definition

Drilling Plans, Agreement to Secure Drilling Rigs, Number of Agreements

+ References

No definition available.

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- Definition

Long Term Commitments Expense Recognized in Statements of Operations

+ References

No definition available.

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- Definition

Recorded Unconditional Purchase Obligation, Market Value

+ References

No definition available.

+ Details

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- Definition

Recorded Unconditional Purchase Obligation, Time Period

+ References

No definition available.

+ Details

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- Definition

The minimum amount the entity agreed to spend under the long-term purchase commitment.

+ References

No definition available.

+ Details

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- Definition

Sets forth the number of units of goods that must be purchased within the specified time period of the agreement to avoid penalties or unfavorable effects on pricing, among other adverse consequences.

+ References

No definition available.

+ Details

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- Definition

Specifies the time period covered by the arrangement.

+ References

No definition available.

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- Definition

The increase (decrease) in the period in loss contingency liabilities.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 5

-Paragraph 9, 10, 11, 12

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-Topic 450

-SubTopic 20

-Section 50

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- Definition

The estimated maximum amount of possible loss from the contingency.

+ References

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

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-Name Accounting Standards Codification

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-SubTopic 20

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 5

-Paragraph 9, 10, 11, 12

-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.

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-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

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- Definition

Total amount of product committed to be supplied under existing contracts or agreements.

+ References

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

-Publisher SEC

-Name Industry Guide

-Number 2

-Paragraph 8

-Subparagraph A

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- Definition

The carrying amount of the long-term purchase obligation as of the balance sheet date, which equals the sum of all payments due.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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-SubTopic 10

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-Paragraph 6

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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-Paragraph 10

-Subparagraph b

-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.

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-Name Accounting Standards Codification

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