No definition available.

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- 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

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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

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Balance Type:	credit
Period Type:	duration

- 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

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Namespace Prefix:	mgee_
Data Type:	num:percentItemType
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- 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

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- 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

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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

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

- Definition

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

+ References

No definition available.

+ Details

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

- References

No definition available.

+ Details

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- 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

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Data Type:	num:percentItemType
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- Definition

Amount of public utility's approved rate increase (decrease) by regulatory agency.

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

Percentage of public utility's approved rate increase (decrease) by regulatory agency.

+ References

No definition available.

+ Details

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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

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

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- 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

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Balance Type:	credit
Period Type:	instant

- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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Rate Matters (Details) - USD ($) $ in Millions	9 Months Ended		12 Months Ended
Rate Matters (Details) - USD ($) $ in Millions	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Aug. 31, 2015
MGE [Member]
Purchased Gas Adjustment [Abstract]
Purchased gas adjustment, overcollection	$ 1.1		$ 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%
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		$ 4.7
PSCW [Member] \| MGE [Member] \| Fuel Rules Surplus Credit, 2015 [Member]
Fuel Rules [Abstract]
Fuel rules, deferred electric cost	$ 7.6
Return of electric fuel credit, current period	$ 0.7
PSCW [Member] \| Total Estimated 2015 Fuel Rules Credit, 2015 [Member] \| MGE [Member] \| Subsequent Event [Member]
Rate Proceedings [Abstract]
Public Utilities Return Of Fuel Rules Surplus Credit Future Period				$ 5.9
PSCW [Member] \| Estimated Return of 2015 Fuel Rules Credit During 2015 [Member] \| MGE [Member] \| Subsequent Event [Member]
Rate Proceedings [Abstract]
Public Utilities Return Of Fuel Rules Surplus Credit Future Period				2.7
PSCW [Member] \| Estimated 2016 Fuel Rules Credit, 2016 [Member] \| MGE [Member] \| Subsequent Event [Member]
Rate Proceedings [Abstract]
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