This amount represents the reduction in fuel rules monitored costs which was approved by the PSCW.

No definition available.

Name:	mgee_Changeinfuelrulesmonitoredcosts
Namespace Prefix:	mgee_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of electric fuel rules monitored costs which have been deferred outside the symmetrical cost tolerance band authorized by a regulatory agency.

+ References

No definition available.

+ Details

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

- Definition

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

+ References

No definition available.

+ Details

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

- Definition

The approved amount ($/kWh) for an electric fuel credit to be returned to customers via a bill credit.

+ References

No definition available.

+ Details

Name:	mgee_Electricfuelcreditperkwh
Namespace Prefix:	mgee_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.

+ Details

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

- Definition

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

+ References

No definition available.

+ Details

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

- Definition

Under fuel rules, the amount in which an entity 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.

+ References

No definition available.

+ Details

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

- Definition

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

+ References

No definition available.

+ Details

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

- Definition

The fuel rules credit that is not required to be refunded to customers and will be amortized. The fuel credit will accrue interest at weighted cost of capital.

+ References

No definition available.

+ Details

Name:	mgee_PublicUtilitiesReturnOfFuelRulesCredit
Namespace Prefix:	mgee_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Effective rate, including composite rate, of cost of financing additions to qualifying regulated assets, commonly called allowance for funds used during construction.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 835
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6501662&loc=d3e56162-110433

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 835
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6501569&loc=d3e55921-110430

+ Details

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

- Definition

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

+ References

No definition available.

+ Details

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

- Definition

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

+ References

No definition available.

+ Details

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

- Definition

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

+ References

No definition available.

+ Details

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

- Definition

Percentage of public utility's approved return on equity.

+ References

No definition available.

+ Details

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

- References

No definition available.

+ Details

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

- Details

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

- Details

Name:	dei_LegalEntityAxis=us-gaap_SubsidiariesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	mgee_ElectricfuelmonitoredcostsyearAxis=mgee_Electricfuelmonitoredcosts2016Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	mgee_FuelRulesCreditYearAxis=mgee_Fuelrulescredit20152016Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	mgee_FuelRulesCreditYearAxis=mgee_Fuelrulesrefund20152016Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	mgee_FuelRulesCreditYearAxis=mgee_Fuelrulescredit2012memberMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementScenarioAxis=us-gaap_ScenarioForecastMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	mgee_ConstructionProjectAxis=mgee_ColumbiaenvironmentalprojectsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
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- Details

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Namespace Prefix:
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Rate Matters (Details) - PSCW [Member] - MGE [Member] - USD ($)	1 Months Ended	4 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jul. 31, 2016	Jan. 31, 2016	Aug. 31, 2015
Rate Proceedings [Abstract]
Authorized return on equity, percentage					10.20%	10.30%
Fuel Rules [Abstract]
Fuel rules, bandwidth				2.00%
Fuel rules, electric fuel costs, deferral, upper threshold				102.00%
Fuel rules, electric fuel costs, deferral, lower threshold				98.00%
Electric Fuel Monitored Costs, 2016 [Member]
Fuel Rules [Abstract]
Change in fuel rules monitored costs								$ (14,800,000)
Deferred fuel rules monitored costs				$ 5,600,000
Fuel Rules Credit ($0.00256/kWh), 2015/2016 [Member]
Fuel Rules [Abstract]
Electric fuel credit (per kWh)		$ 0.00256		0.00256
Electric fuel credit ($)									$ 10,900,000
Return of electric fuel credit, total		$ 2,600,000		$ 8,300,000
Fuel Rules Refund, 2015/2016 [Member] \| Electric Fuel Monitored Costs, 2016 [Member]
Fuel Rules [Abstract]
Electric fuel credit ($)							$ 15,700,000
Return of electric fuel credit, total	$ 15,500,000
Fuel Rules Credit, 2012 [Member]
Fuel Rules [Abstract]
Return of electric fuel credit, total						$ 6,300,000
Approved Future Rate Matters [Member]
Rate Proceedings [Abstract]
Approved equity capital structure, percentage			57.20%
Authorized return on equity, percentage			9.80%
Columbia Environmental Projects [Member]
Rate Proceedings [Abstract]
Authorized AFUDC rate					100.00%	100.00%
Electric Rate Proceeding [Member]
Rate Proceedings [Abstract]
Authorized rate increase (decrease), percentage				0.00%	3.80%	0.00%
Authorized rate increase (decrease), amount				$ 0	$ 15,400,000	$ 0
Electric Rate Proceeding [Member] \| Approved Future Rate Matters [Member]
Rate Proceedings [Abstract]
Authorized rate increase (decrease), percentage			(0.80%)
Authorized rate increase (decrease), amount			$ (3,300,000)
Gas Rate Proceeding [Member]
Rate Proceedings [Abstract]
Authorized rate increase (decrease), percentage				0.00%	(2.00%)	0.00%
Authorized rate increase (decrease), amount				$ 0	$ (3,800,000)	$ 0
Gas Rate Proceeding [Member] \| Approved Future Rate Matters [Member]
Rate Proceedings [Abstract]
Authorized rate increase (decrease), percentage			1.90%
Authorized rate increase (decrease), amount			$ 3,100,000