No definition available.

Name:	mgee_FuelRulesAbstract
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

The amount of electric fuel-related costs in which an entity has deferred outside the symmetrical cost tolerance band authorized by a regulatory agency in the most recent rate order.

+ References

No definition available.

+ Details

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

- Definition

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.

+ References

No definition available.

+ Details

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

- Definition

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

+ References

No definition available.

+ Details

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

- Definition

The fuel rules surplus credit that will be refunded to customers during future periods.

+ References

No definition available.

+ Details

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

- Definition

The fuel rules surplus 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_PublicUtilitiesReturnOfFuelRulesSurplusCredit
Namespace Prefix:	mgee_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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

+ References

No definition available.

+ Details

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

- References

No definition available.

+ Details

Name:	mgee_PurchasedGasAdjustmentAbstract
Namespace Prefix:	mgee_
Data Type:	xbrli:stringItemType
Balance Type:	na
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

Name:	us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionRate
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

Name:	us-gaap_PublicUtilitiesApprovedRateIncreaseDecreaseAmount
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

- Definition

Gas costs of a regulated entity that are refundable through future rate adjustments. Such costs are a form of a regulatory liabilities and are expected to be refunded in less than one year through rate adjustments.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 405

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.20)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_RefundableGasCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

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

- Details

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

- Details

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

- Details

Name:	mgee_FuelRulesSurplusCreditYearAxis=mgee_FuelRulesSurplusCredit2012Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementScenarioAxis=mgee_ProposedTotalEstimated2015FuelRulesCredit2016Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_StatementScenarioAxis=mgee_ProposedEstimatedReturnOf2015FuelRulesCreditDuring2015Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementScenarioAxis=mgee_ProposedEstimated2016FuelRulesCredit2016Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

Rate Matters (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
Rate Matters (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014	Jul. 31, 2015	Jun. 30, 2014
MGE [Member]
Purchased Gas Adjustment [Abstract]
Purchased gas adjustment, overcollection	$ 4.0	$ 1.2
PSCW [Member] \| Legal Entity Type of Counterparty [Domain]
Fuel Rules [Abstract]
Fuel rules, bandwidth	2.00%
Fuel rules, electric fuel deferred costs upper threshold	102.00%
Fuel rules, electric fuel deferred costs lower threshold	98.00%
PSCW [Member] \| MGE [Member]
Rate Proceedings [Abstract]
Authorized return on equity, percentage	10.20%	10.30%
Fuel Rules [Abstract]
Fuel rules, deferred electric cost	$ 5.7
PSCW [Member] \| MGE [Member] \| Fuel Rules Surplus Credit, 2012 [Member]
Rate Proceedings [Abstract]
Return of electric fuel credit, total		$ 6.3
Fuel Rules [Abstract]
Return of electric fuel credit, current period				$ 3.2
PSCW [Member] \| Proposed Total Estimated 2015 Fuel Rules Credit, 2016 [Member] \| MGE [Member] \| Subsequent Event [Member]
Rate Proceedings [Abstract]
Proposed Public Utilities Return Of Fuel Rules Surplus Credit Future Period			$ 5.9
PSCW [Member] \| Proposed Estimated Return of 2015 Fuel Rules Credit During 2015 [Member] \| MGE [Member] \| Subsequent Event [Member]
Rate Proceedings [Abstract]
Proposed Public Utilities Return Of Fuel Rules Surplus Credit Future Period			2.7
PSCW [Member] \| Proposed Estimated 2016 Fuel Rules Credit, 2016 [Member] \| MGE [Member] \| Subsequent Event [Member]
Rate Proceedings [Abstract]
Proposed Public Utilities Return Of Fuel Rules Surplus Credit Future Period			$ 5.0
PSCW [Member] \| Columbia Environmental Project [Member] \| MGE [Member]
Rate Proceedings [Abstract]
Authorized AFUDC Rate		100.00%
Electric [Member] \| PSCW [Member] \| MGE [Member]
Rate Proceedings [Abstract]
Authorized rate increase (decrease), percentage	3.80%	0.00%
Authorized rate increase (decrease), amount	$ 15.4	$ 0.0
Gas [Member] \| PSCW [Member] \| MGE [Member]
Rate Proceedings [Abstract]
Authorized rate increase (decrease), percentage	(2.00%)	0.00%
Authorized rate increase (decrease), amount	$ (3.8)	$ 0.0