Commitments and Contingencies (Details-1) (USD $) In Millions, unless otherwise specified	6 Months Ended
Jun. 30, 2013
Columbia Clean Air Act Litigation [Abstract]
Columbia Clean Air Act litigation civil penalties	$ 0.2
Columbia Clean Air Act litigation environmental mitigation costs	0.6
Columbia Environmental Project [Member]
Expected Capital Expenditures [Line Items]
MGE's total share of expected capital expenditures	140.0
Columbia Commitments [Abstract]
Columbia environmental project commitments	$ 38.6
Columbia Units [Member]
Jointly Owned Utility Plant Interests [Line Items]
Generating capability - MW	225
Columbia's share of MGE's net generating capability	29.00%
Ownership interest in jointly owned plant	22.00%
WPL ownership interest of Columbia	46.20%
WPSC ownership interest of Columbia	31.80%

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

This element represents the expenses incurred by the entity which are directly related to settlement of litigation.

+ References

No definition available.

+ Details

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

- Definition

This element represents the approximate costs of environmental mitigation projects agreed to in the terms of the final consent decree.

+ References

No definition available.

+ Details

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

- Details

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

- Definition

Committed Columbia environmental project commitments.

+ References

No definition available.

+ Details

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

- Definition

Expected capital expenditures to be incurred during construction of an asset.

+ References

No definition available.

+ Details

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

- Details

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

- Definition

A jointly owned utility plant's share of MGE's net generating capability.

+ References

No definition available.

+ Details

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

- Definition

MGE's portion of the total operating capacity (in MWs) of each of the two units in the jointly owned utility plant.

+ References

No definition available.

+ Details

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

- Definition

WPL's proportionate share of interest (percent) in Columbia, a jointly owned utility plant.

+ References

No definition available.

+ Details

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

- Definition

WPSC's proportionate share of interest (percent) in Columbia, a jointly owned utility plant.

+ References

No definition available.

+ Details

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

- Details

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

- Definition

The proportionate share of interest (percent) in a jointly owned utility plant.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 360

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 10.C)

-URI http://asc.fasb.org/extlink&oid=6500719&loc=d3e659983-123033

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

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 10

-Section C

+ Details

Name:	us-gaap_JointlyOwnedUtilityPlantProportionateOwnershipShare
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant