Commitments and Contingencies (Details-4) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2013
Columbia Environmental Project [Member] \| MGE [Member]
Columbia
Jointly owned utility plant, total expected capital expenditures	$ 135.0
Columbia Units [Member]
Columbia
Contractual commitments	14.7
Envrionmental civil penalty expense	0.2
Accrual for future environmental mitigation projects	$ 0.6
Wisconsin Energy Efficiency and Renewables Act [Member]
Energy Efficiency and Renewables
Minimum electricity generated from renewable resources by 2015	10.00%
Clean Air Interstate Rule [Member]
Air Quality
Minimum capacity of fossil-fuel fired electric generating units required to meet certain air quality regulations (in MW)	25
Fossil-fuel EGU emission reduction levels as compared to 2003, phase two (beginning in 2015), NOx	65.00%
Fossil-fuel EGU emission reduction levels as compared to 2003, phase two (beginning in 2015), SO2	70.00%

Accrual for future environmental mitigation projects as a result of environmental regulation violations.

No definition available.

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

- Details

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Namespace Prefix:	mgee_
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- Details

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Namespace Prefix:	mgee_
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- Details

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Namespace Prefix:	mgee_
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Balance Type:	na
Period Type:	duration

- Definition

Civil penalty expense related to environmental regulation violations.

+ References

No definition available.

+ Details

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

- Definition

Total expected capital expenditures to be incurred during construction of an asset.

+ References

No definition available.

+ Details

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

- Definition

The minimum capacity of fossil-fuel fired electric generating units required to abide by certain air quality regulations as deemed by a regulatory agency.

+ References

No definition available.

+ Details

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Namespace Prefix:	mgee_
Data Type:	num:powerItemType
Balance Type:	na
Period Type:	instant

- Definition

The reduction of annual regional emission for NOx under the second phase (beginning in 2015) as required by teh regulatory agency.

+ References

No definition available.

+ Details

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Namespace Prefix:	mgee_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The reduction of annual regional emission for SO2 under the second phase (beginning in 2015) as required by the regulatory agency.

+ References

No definition available.

+ Details

Name:	mgee_PublicUtilitiesAirQualityRegulationsPhaseTwoRequired2015FossilFuelElectricGeneratingUnitEmissionReductionLevelsAsComparedTo2003SulfurOxide
Namespace Prefix:	mgee_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The minimum electricity generated from renewable resources by 2015 set by regulatory agency

+ References

No definition available.

+ Details

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Namespace Prefix:	mgee_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

+ References

No definition available.

+ Details

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