Commitments and Contingencies (Details-2) (USD $)	9 Months Ended
Sep. 30, 2011 MW Tons Dth MWh
Chattel Paper Purchase Agreement [Abstract]
Chattel paper purchase agreement maximum interest	$ 10,000,000
Outstanding interest in chattel paper receivables	4,500,000
Servicing asset recognized	200,000
Wind Development Rights [Abstract]
Wind development rights capacity (in MWs)	175
Wind development rights payments to be returned	2,000,000
Wind development rights unpaid balance	1,800,000
Smart Grid Investment Grant [Abstract]
Smart Grid grant approval amount	5,500,000
Total cost of proposed projects	11,000,000
Smart grid expenditures to date	4,900,000
One Year From Balance Sheet Date [Member]
Chattel Paper Agreement Principal Payments [Abstract]
Chattel paper agreement principal payments	145,000
Coal Commitments [Abstract]
Coal commitments	6,264,000
Natural Gas Commitments [Abstract]
Natural gas transportation and storage commitments	4,897,000
Natural gas supply commitments	15,797,000
Total purchase contracts	26,958,000
Wind Development Rights [Abstract]
Wind development payments expected to receive	900,000
Smart Grid Investment Grant [Abstract]
Smart grid commitments to date	600,000
More Than One And Within Two Years From Balance Sheet Date [Member]
Chattel Paper Agreement Principal Payments [Abstract]
Chattel paper agreement principal payments	588,000
Coal Commitments [Abstract]
Coal commitments	24,374,000
Natural Gas Commitments [Abstract]
Natural gas transportation and storage commitments	17,285,000
Natural gas supply commitments	14,841,000
Total purchase contracts	56,500,000
Wind Development Rights [Abstract]
Wind development payments expected to receive	900,000
More Than Two And Within Three Years From Balance Sheet Date [Member]
Chattel Paper Agreement Principal Payments [Abstract]
Chattel paper agreement principal payments	630,000
Coal Commitments [Abstract]
Coal commitments	18,769,000
Natural Gas Commitments [Abstract]
Natural gas transportation and storage commitments	17,037,000
Natural gas supply commitments	0
Total purchase contracts	35,806,000
More Than Three And Within Four Years From Balance Sheet Date [Member]
Chattel Paper Agreement Principal Payments [Abstract]
Chattel paper agreement principal payments	444,000
Coal Commitments [Abstract]
Coal commitments	3,670,000
Natural Gas Commitments [Abstract]
Natural gas transportation and storage commitments	16,843,000
Natural gas supply commitments	0
Total purchase contracts	20,513,000
More Than Four And Within Five Years From Balance Sheet Date [Member]
Chattel Paper Agreement Principal Payments [Abstract]
Chattel paper agreement principal payments	754,000
Coal Commitments [Abstract]
Coal commitments	0
Natural Gas Commitments [Abstract]
Natural gas transportation and storage commitments	16,689,000
Natural gas supply commitments	0
Total purchase contracts	$ 16,689,000

Chattel paper agreement principal payments.

Name:	mgee_ChattelPaperAgreementPrincipalPayments
Namespace Prefix:	mgee
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	mgee_ChattelPaperAgreementPrincipalPaymentsAbstract
Namespace Prefix:	mgee
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	mgee_ChattelPaperPurchaseAgreementAbstract
Namespace Prefix:	mgee
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

MGE is party to a chattel paper purchase agreement with a financial institution under which it can sell or finance an undivided interest with recourse, in up to $10.0 million of the financing program receivables, until August 31, 2011.

+ Details

Name:	mgee_ChattelPaperPurchaseAgreementMaximumInterest
Namespace Prefix:	mgee
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Coal commitments for the Columbia and Elm Road Units.

+ Details

Name:	mgee_CoalCommitments
Namespace Prefix:	mgee
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	mgee_CoalCommitmentsAbstract
Namespace Prefix:	mgee
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	mgee_NaturalGasCommitmentsAbstract
Namespace Prefix:	mgee
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Natural gas supply commitments.

+ Details

Name:	mgee_NaturalGasSupplyCommitments
Namespace Prefix:	mgee
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Natural gas transportation and storage commitments.

+ Details

Name:	mgee_NaturalGasTransportationAndStorageCommitments
Namespace Prefix:	mgee
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Outstanding interest in chattel paper interest receivables.

+ Details

Name:	mgee_OutstandingInterestInChattelPaperReceivables
Namespace Prefix:	mgee
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Total purchase contracts.

+ Details

Name:	mgee_PurchaseContractsNet
Namespace Prefix:	mgee
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Smart grid commitments.

+ Details

Name:	mgee_SmartGridCommitments
Namespace Prefix:	mgee
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Expenditures incurred related to the smart grid projects.

+ Details

Name:	mgee_SmartGridExpenditures
Namespace Prefix:	mgee
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

MGE approved grant for smart grid projects by the U.S. Department of Energy (DOE) under the federal stimulus program.

+ Details

Name:	mgee_SmartGridGrantAmount
Namespace Prefix:	mgee
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	mgee_SmartGridInvestmentGrantAbstract
Namespace Prefix:	mgee
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Total cost of the proposed smart grid project including the grant approved by the U.S. Department of Energy (DOE) under the federal stimulus program.

+ Details

Name:	mgee_TotalCostOfProposedProjects
Namespace Prefix:	mgee
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Payments expected to receive for the wind development rights.

+ Details

Name:	mgee_WindDevelopmentPaymentsExpectedToReceive
Namespace Prefix:	mgee
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	mgee_WindDevelopmentRightsAbstract
Namespace Prefix:	mgee
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Potential capacity in megawatts of wind development rights in Iowa.

+ Details

Name:	mgee_WindDevelopmentRightsCapacity
Namespace Prefix:	mgee
Data Type:	num:volumeItemType
Balance Type:	na
Period Type:	instant

- Definition

Payments made on wind development rights that will be returned to MAGAEL, LLC.

+ Details

Name:	mgee_WindDevelopmentRightsPaymentsToBeReturned
Namespace Prefix:	mgee
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Remaining unpaid balance on wind development rights payment.

+ Details

Name:	mgee_WindDevelopmentRightsUnpaidBalance
Namespace Prefix:	mgee
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amortized carrying amount (balance) as of the balance sheet date of an asset representing net future revenues from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 50

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122501-111745

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 50

-Section 50

-Paragraph 4

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6863725&loc=d3e122739-111746

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 140

-Paragraph 17

-Subparagraph g(1)(a)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 50

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122492-111745

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 140

-Paragraph 13A, 13B

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 50

-Section 25

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6777056&loc=d3e120260-111741

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS140-4/FIN46(R)-8

-Paragraph B10

-Subparagraph a(1)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Name:	us-gaap_ServicingAssetAtAmortizedValue
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant