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

The amount of fuel savings approved by the PSCW for an electric fuel credit to be returned to customers via a bill credit.

No definition available.

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

- References

No definition available.

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

Pursuant to the provisions of the rate order, the fuel rules bandwidth will be plus or minus this percentage.

No definition available.

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

Under fuel rules, the amount in which MGE is required to defer the benefit of lower costs if actual electric fuel costs were less than the allowed electric fuel costs in latest rate order.

No definition available.

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

Under fuel rules, the amount in which MGE would defer if actual electric fuel costs exceeded allowed electric fuel costs in latest rate order.

No definition available.

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

Percentage of public utility's approved equity to capital, including debt and equity.

No definition available.

Name:	us-gaap_PublicUtilitiesApprovedEquityCapitalStructurePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Amount of public utility's approved rate increase (decrease) by regulatory agency.

No definition available.

Name:	us-gaap_PublicUtilitiesApprovedRateIncreaseDecreaseAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Percentage of public utility's approved rate increase (decrease) by regulatory agency.

No definition available.

Name:	us-gaap_PublicUtilitiesApprovedRateIncreaseDecreasePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Percentage of public utility's approved return on equity.

No definition available.

Name:	us-gaap_PublicUtilitiesApprovedReturnOnEquityPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

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

Percentage of public utility's requested rate increase (decrease) with regulatory agency.

No definition available.

Name:	us-gaap_PublicUtilitiesRequestedRateIncreaseDecreasePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 340
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382

Name:	us-gaap_RegulatoryAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

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

Name:	us-gaap_RegulatoryAssetAxis=mgee_DeferredCovidNineteenExpendituresMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_RegulatoryAgencyAxis=mgee_PublicServiceCommissionOfWisconsinMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

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

Name:	mgee_FuelRulesCreditYearAxis=mgee_FuelRulesRefund2018Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_PublicUtilitiesRegulatoryProceedingAxis=mgee_ElectricRateProceedingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: