Long-Term Debt and Notes Payable (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010
Debt Instrument [Line Items]
Long-term debt	$ 1,155,246	$ 410,793
Less amounts due within one year	1,000	5,000
Less unamortized debt discount	546	539
Long-term debt, excluding current maturities	1,153,700	405,254
Medium-term Notes \| Medium-term Notes, Series A and B, interest ranging from 7.125% to 7.6%, for notes due July 30, 2012 to February 15, 2028
Debt Instrument [Line Items]
Long-term debt	155,000	155,000
Debt instrument, interest rate, minimum	7.125%
Debt instrument, interest rate, maximum	7.60%
Medium-term Notes \| Medium-term Notes, Series A, interest of 7.57%
Debt Instrument [Line Items]
Debt instrument, interest rate		7.57%
Notes \| 5% Notes, due October 1, 2013
Debt Instrument [Line Items]
Long-term debt	50,000	50,000
Debt instrument, interest rate	5.00%
Senior Notes \| 4.625% Notes, due September 1, 2021
Debt Instrument [Line Items]
Long-term debt	400,000	0
Debt instrument, interest rate	4.625%
Senior Term Loans \| Senior Term Loans, (floating rate interest LIBOR plus 1.375%; currently 1.67% at December 31, 2011), due March 31, 2014 to November 29, 2016
Debt Instrument [Line Items]
Long-term debt	300,000	0
Debt Instrument, basis spread on variable rate	1.375%
Floating rate interest, plus basis points	1.67%
Alabama Gas Corporation
Debt Instrument [Line Items]
Less amounts due within one year	0	5,000
Long-term debt, excluding current maturities	250,246	200,793
Alabama Gas Corporation \| Medium-term Notes \| Medium-term Notes, Series A, interest of 7.57%
Debt Instrument [Line Items]
Long-term debt	0	5,000
Alabama Gas Corporation \| Notes \| 5.20% Notes, due January 15, 2020
Debt Instrument [Line Items]
Long-term debt	40,000	40,000
Debt instrument, interest rate	5.20%
Alabama Gas Corporation \| Notes \| 5.70% Notes, due January 15, 2035
Debt Instrument [Line Items]
Long-term debt	35,246	35,793
Debt instrument, interest rate	5.70%
Alabama Gas Corporation \| Notes \| 5.368% Notes, due December 1, 2015
Debt Instrument [Line Items]
Long-term debt	80,000	80,000
Debt instrument, interest rate	5.368%
Alabama Gas Corporation \| Notes \| 5.90% Notes, due January 15, 2037
Debt Instrument [Line Items]
Long-term debt	45,000	45,000
Debt instrument, interest rate	5.90%
Alabama Gas Corporation \| Notes \| 3.86% Notes, due December 21, 2021
Debt Instrument [Line Items]
Long-term debt	$ 50,000	$ 0
Debt instrument, interest rate	3.86%

The percentage points added to the reference rate to compute the variable rate on the debt instrument.

No definition available.

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- Definition

Interest rate stated in the contractual debt agreement.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

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- Definition

When presenting a range of interest rates, the highest stated (contractual) rate for funds borrowed under the debt agreement as of the balance sheet date.

+ References

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- Definition

When presenting a range of interest rates, the lowest stated (contractual) rate for funds borrowed under the debt agreement as of the balance sheet date.

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-Name Regulation S-X (SX)

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- Definition

The amount of debt discount that was originally recognized at the issuance of the instrument that has yet to be amortized.

+ References

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-Publisher FASB

-Name FASB Staff Position (FSP)

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-Paragraph 31

-Subparagraph b

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- Definition

Including current and noncurrent portions, aggregate carrying amount of long-term borrowings as of the balance sheet date. May include notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, which had initial maturities beyond one year or beyond the normal operating cycle, if longer, and after deducting unamortized discount or premiums, if any.

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- Definition

Total of the portions of the carrying amounts as of the balance sheet date of long-term debt, which may include notes payable, bonds payable, debentures, mortgage loans, and commercial paper, which are scheduled to be repaid within one year or the normal operating cycle, if longer, and after deducting unamortized discount or premiums, if any.

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Sum of the carrying values as of the balance sheet date of all long-term debt, which is debt initially having maturities due after one year from the balance sheet date or beyond the operating cycle, if longer, but excluding the portions thereof scheduled to be repaid within one year (current maturities) or the normal operating cycle, if longer, and after deducting unamortized discount or premiums, if any.

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The interest rate applicable to the portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a rate subject to change from time to time.

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