Fair Value of Financial Instruments (Details-2) (USD $)	9 Months Ended
Sep. 30, 2011	Dec. 31, 2010
Deferred compensation interest calculation [Abstract]
U.S Treasury Bills maturity	26
Increase compounded monthly	1.00%
Minimum annual rate	7.00%
Liabilities:
Derivative collateral	$ 400,000	$ 500,000
MGE Energy [Member]
Assets:
Exchange-traded investments	386,000	430,000
Total Assets	386,000	430,000
Liabilities:
Derivatives, net	26,583,000	19,230,000
Deferred compensation	1,660,000	1,525,000
Total liabilities	28,243,000	20,755,000
Derivative collateral	400,000	500,000
MGE Energy [Member] \| Level 1 [Member]
Assets:
Exchange-traded investments	386,000	430,000
Total Assets	386,000	430,000
Liabilities:
Derivatives, net	673,000	14,000
Deferred compensation	1,660,000	1,525,000
Total liabilities	2,333,000	1,539,000
MGE Energy [Member] \| Level 2 [Member]
Assets:
Exchange-traded investments	0	0
Total Assets	0	0
Liabilities:
Derivatives, net	0	0
Deferred compensation	0	0
Total liabilities	0	0
MGE Energy [Member] \| Level 3 [Member]
Assets:
Exchange-traded investments	0	0
Total Assets	0	0
Liabilities:
Derivatives, net	25,910,000	19,216,000
Deferred compensation	0	0
Total liabilities	25,910,000	19,216,000
MGE [Member]
Assets:
Exchange-traded investments	170,000	260,000
Total Assets	170,000	260,000
Liabilities:
Derivatives, net	26,583,000	19,230,000
Deferred compensation	1,660,000	1,525,000
Total liabilities	28,243,000	20,755,000
Derivative collateral	400,000	500,000
MGE [Member] \| Level 1 [Member]
Assets:
Exchange-traded investments	170,000	260,000
Total Assets	170,000	260,000
Liabilities:
Derivatives, net	673,000	14,000
Deferred compensation	1,660,000	1,525,000
Total liabilities	2,333,000	1,539,000
MGE [Member] \| Level 2 [Member]
Assets:
Exchange-traded investments	0	0
Total Assets	0	0
Liabilities:
Derivatives, net	0	0
Deferred compensation	0	0
Total liabilities	0	0
MGE [Member] \| Level 3 [Member]
Assets:
Exchange-traded investments	0	0
Total Assets	0	0
Liabilities:
Derivatives, net	25,910,000	19,216,000
Deferred compensation	0	0
Total liabilities	$ 25,910,000	$ 19,216,000

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Percentage increase compounded monthly used in deferred compensation interest calculation.

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- Definition

Minimum annual rate used in deferred compensation interest calculation.

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- Definition

Treasury Bills maturity used in deferred compensation interest calculation (in weeks).

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- Definition

This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 12

-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.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6379932&loc=d3e22054-111558

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Available-for-Sale Securities

-URI http://asc.fasb.org/extlink&oid=6505594

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- Definition

The amount of the right to reclaim cash collateral under master netting arrangements that have not been offset against net derivative instrument positions.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=6935481&loc=d3e41678-113959

-Subparagraph (b)

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- Definition

Derivative instrument obligations meeting the definition of a liability which the Company is a party to as of the balance sheet date.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 10

-Subparagraph i

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 6

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 15

-Paragraph 83

-URI http://asc.fasb.org/extlink&oid=6913464&loc=d3e34841-113949

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This element represents the aggregate of the liabilities reported on the balance sheet at period end measured at fair value by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

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