Commitments and Contingencies (Details-2) (Chattel Paper Agreement [Member], USD $)	9 Months Ended
Sep. 30, 2014
Guarantor Obligations [Line Items]
Guarantor obligation, maximum financing receivable	$ 10,000,000
Guarantor obligation, current carrying value	4,100,000
Servicing asset recognized	200,000
Guarantor Obligation, Fiscal Year Maturity [Abstract]
Guarantor obligation, 2014	108,000
Guarantor obligation, 2015	921,000
Guarantor obligation, 2016	841,000
Guarantor obligation, 2017	438,000
Guarantor obligation, 2018	$ 374,000
Minimum [Member]
Guarantor Obligations [Line Items]
Guarantee to financial institution, term	1 year
Maximum [Member]
Guarantor Obligations [Line Items]
Guarantee to financial institution, term	10 years

Amount of guarantor obligation maturing in the fifth fiscal year following the latest fiscal year.

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of guarantor obligation maturing in the fourth fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- Definition

Amount of guarantor obligation maturing in the second fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- Definition

Amount of guarantor obligation maturing in the third fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

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Namespace Prefix:	mgee_
Data Type:	xbrli:monetaryItemType
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- Details

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- Definition

Amount of guarantor obligation maturing in the remainder of the fiscal year following the latest fiscal year ended.

+ References

No definition available.

+ Details

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

- Definition

Term of guarantor obligation.

+ References

No definition available.

+ Details

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Namespace Prefix:	mgee_
Data Type:	xbrli:durationItemType
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- Definition

The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 460

-SubTopic 10

-Section 50

-Paragraph 4

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12069-110248

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_GuaranteeObligationsLineItems
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Balance Type:	na
Period Type:	duration

- Definition

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 460

-SubTopic 10

-Section 50

-Paragraph 4

-Subparagraph (b)(1)

-URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12069-110248

+ Details

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

Amortized amount of contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.

+ References

Reference 1: 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=7524895&loc=d3e120260-111741

Reference 2: 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 3: 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 4: 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=7882072&loc=d3e122739-111746

+ Details

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Balance Type:	debit
Period Type:	instant