Name:	mgee_FairValueInputsAssetsQuantitativeInformationLineItems
Namespace Prefix:	mgee_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Name:	mgee_FairValueInputsCounterpartyFuelMixAbstract
Namespace Prefix:	mgee_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Estimate of counterparty's internal generation as a portion of their fuel mix, used as an input to measure fair value.

+ References

No definition available.

+ Details

Name:	mgee_FairValueInputsCounterpartyFuelMixInternalGeneration
Namespace Prefix:	mgee_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Estimate of counterparty's purchased power as a portion of their fuel mix, used as an input to measure fair value.

+ References

No definition available.

+ Details

Name:	mgee_FairValueInputsCounterpartyFuelMixPurchasedPower
Namespace Prefix:	mgee_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Basis adjustment between delivery points for off peak electric future prices. Used as an input to measure fair value.

+ References

No definition available.

+ Details

Name:	mgee_FairValueInputsDeliveryPointsBasisAdjustmentOffPeak
Namespace Prefix:	mgee_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Basis adjustment between delivery points for on peak electric future prices. Used as an input to measure fair value.

+ References

No definition available.

+ Details

Name:	mgee_FairValueInputsDeliveryPointsBasisAdjustmentOnPeak
Namespace Prefix:	mgee_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

+ References

No definition available.

+ Details

Name:	mgee_LongTermDebtFairValueDisclosure
Namespace Prefix:	mgee_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

+ References

No definition available.

+ Details

Name:	mgee_ShortTermDebtCommercialPaperFairValueDisclosure
Namespace Prefix:	mgee_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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 includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Company may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash

-URI http://asc.fasb.org/extlink&oid=6506951

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

-URI http://asc.fasb.org/extlink&oid=6507016

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 7, 8, 9, 10

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 7

-Footnote 1

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 8

-Footnote 2

-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.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FinancialInstrumentsFinancialLiabilitiesBalanceSheetGroupingsAbstract
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Data Type:	xbrli:stringItemType
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Fair Value of Financial Instruments (Details-1) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2013 Maximum [Member]	Mar. 31, 2013 Minimum [Member]	Mar. 31, 2013 Carrying Amount [Member]	Dec. 31, 2012 Carrying Amount [Member]	Mar. 31, 2013 Fair Value [Member]	Dec. 31, 2012 Fair Value [Member]	Mar. 31, 2013 MGE [Member] Carrying Amount [Member]	Dec. 31, 2012 MGE [Member] Carrying Amount [Member]	Mar. 31, 2013 MGE [Member] Fair Value [Member]	Dec. 31, 2012 MGE [Member] Fair Value [Member]
Assets:
Cash and cash equivalents				$ 45,894	$ 46,357	$ 45,894	$ 46,357	$ 9,856	$ 6,350	$ 9,856	$ 6,350
Liabilities:
Short-term debt - commercial paper				10,500	0	10,500	0	10,500	0	10,500	0
Long-term debt				$ 361,138	$ 361,805	$ 432,430	$ 427,456	$ 361,138	$ 361,805	$ 432,430	$ 427,456
Significant unobservable inputs [Line Items]
Basis adjustment - on peak	97.10%
Basis adjustment - off peak	96.00%
Counterparty fuel mix [Abstract]
Internal generation		70.00%	50.00%
Purchased power		50.00%	30.00%