The common equity ratio, calculated on a thirteen month rolling average.

No definition available.

Name:	mgee_CommonEquityRatio
Namespace Prefix:	mgee_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

The minimum common equity ratio required to avoid dividend payment restirctions to the parent company.

+ References

No definition available.

+ Details

Name:	mgee_CommonEquityRatioDividendRestrictionThreshold
Namespace Prefix:	mgee_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

The total amount of dividends available under covenant terms

+ References

No definition available.

+ Details

Name:	mgee_DebtInstrumentCovenantTermsAllowableAmountAvailableForDividendPayment
Namespace Prefix:	mgee_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- References

No definition available.

+ Details

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

- 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.

+ References

No definition available.

+ Details

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

- Definition

This element represents disclosure of the aggregate cash dividends paid to the entity by consolidated subsidiaries.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04(b))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690

+ Details

Name:	us-gaap_CashDividendsPaidToParentCompanyByConsolidatedSubsidiaries
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	srt_ConsolidatedEntitiesAxis=srt_ParentCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=mgee_FirstMortgageBondsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=mgee_SevenPointSevenZeroPercentFirstMortgageBondsDue2028Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=mgee_MgeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=mgee_MgePowerElmRoadMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=mgee_MgePowerWestCampusMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=mgee_MgeTranscoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=mgee_MgeetranscoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=mgee_NgvfuelingservicesmemberMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Schedule I - Condensed Parent Company Finanical Statements (Details-Notes 2)	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
MGE Energy [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	$ 28,246,000	$ 26,735,000	$ 67,781,000
First Mortgage Bonds [Member] \| 7.70%, 2028 Series
Dividend Restrictions
Debt covenant, allowable amount available for payment of dividends	465,200,000
MGE [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	$ 0	0	45,000,000
Dividend Restrictions
Common equity ratio	0.573
MGE [Member] \| Minimum [Member]
Dividend Restrictions
Dividend restrictions, common equity ratio	0.55
MGE Power Elm Road [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	$ 15,500,000	15,500,000	12,000,000
MGE Power West Campus [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	8,000,000	6,500,000	6,000,000
MGE Transco [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	4,653,000	4,625,000	4,669,000
MGEE Transco [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	93,000	60,000	112,000
NGV Fueling Services [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	$ 0	$ 50,000	$ 0