Equity and Financing Arrangements (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
Sep. 30, 2011
MGE Power Elm Road Issued Debt [Abstract]
Issuance of secured long-term debt	$ 30.0
Maturity date	Feb. 25, 2041
Interest rate on secured long-term debt	4.74%
Debt service coverage ratio range, high	1.25
Debt service coverage ratio range, low	1.00
MGE Energy [Member]
Credit Facilities [Line Items]
Revolving credit facility	40.0
LIBOR-based borrowings adder	0.85%
MGE [Member]
Credit Facilities [Line Items]
Revolving credit facility	$ 75.0
LIBOR-based borrowings adder	0.85%

Debt service covereage ratio that must be maintained for a trailing 12-month period.

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- Definition

Debt service covereage ratio that must be maintained for a trailing 12-month period.

+ Details

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- Definition

Borrowings under credit agreements may bear interest at a rate that floats daily based upon a LIBOR-based index. Depending on the current senior unsecured credit rating, an adder may be required.

+ Details

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- Details

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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

-Paragraph 22

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

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- Definition

Date when the debt instrument is scheduled to be fully repaid, which may be presented in a variety of ways (year, month and year, day, month and year, quarter, etc.).

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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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-Subparagraph (SX 210.5-02.22(a)(2))

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

-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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-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

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- Definition

The cash inflow from amounts received from issuance of long-term debt that is wholly or partially secured by collateral. Excludes proceeds from tax exempt secured debt.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

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-Glossary Financing Activities

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+ Details

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