Investment in ATC (Details-1) (USD $)	9 Months Ended		4 Months Ended
Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 MGE Transco [Member] ATC [Member]	Sep. 30, 2012 MGE Transco [Member] ATC [Member]	Dec. 31, 2012 MGE Transco [Member] ATC [Member]	Oct. 31, 2013 MGE Transco [Member] ATC [Member] Subsequent Event [Member]
Schedule Of Equity Method Investments [Line Items]
Equity earnings from investment	$ 7,045,000	$ 6,764,000	$ 7,000,000	$ 6,800,000
Dividend income from investment	5,498,000	5,300,000	5,500,000	5,300,000
Capital contributions to investment	1,305,000	1,988,000	1,100,000	1,800,000		400,000
Equity method investment			$ 63,600,000		$ 61,000,000

This item represents disclosure of the amount of dividends or other distributions received from unconsolidated subsidiaries, certain corporate joint ventures, and certain noncontrolled corporation; these investments are accounted for under the equity method of accounting. This element excludes distributions that constitute a return of investment, which are classified as investing activities.

+ References+ Details

This item represents the entity's proportionate share for the period of the net income (loss) of its investee (such as unconsolidated subsidiaries and joint ventures) to which the equity method of accounting is applied. This item includes income or expense related to stock-based compensation based on the investor's grant of stock to employees of an equity method investee.

+ References

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

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 323

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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Reference 8: http://www.xbrl.org/2003/role/presentationRef

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+ Details