Equity and Financing Arrangements (Details) - USD ($)	9 Months Ended
Sep. 30, 2015	Sep. 30, 2014
Common Stock [Abstract]
Common stock issued during period	0	0
Dilutive Shares Calculation [Abstract]
Dilutive securities	$ 0
MGE [Member]
Credit Facilities [Line Items]
Commercial paper outstanding	0
MGE [Member] \| MGE $60 million unsecured committed revolving line of credit
Credit Facilities [Line Items]
Available lines of credit	60,000,000
Line of credit, borrowings outstanding	$ 0
Line Of Credit Facility Fixed Base Rate For Federal Funds	0.50%
Line Of Credit Facility Fixed Base Rate For Eurodollar Rate	1.00%
MGE [Member] \| MGE $60 million unsecured committed revolving line of credit \| Minimum [Member]
Credit Facilities [Line Items]
Line Of Credit Facility Floating Rate Based Adder	0.00%
Line Of Credit Facility Eurodollar Based Adder	0.625%
MGE [Member] \| MGE $60 million unsecured committed revolving line of credit \| Maximum [Member]
Credit Facilities [Line Items]
Line Of Credit Facility Floating Rate Based Adder	0.125%
Line Of Credit Facility Eurodollar Based Adder	1.125%
MGE [Member] \| MGE $40 million unsecured committed revolving line of credit
Credit Facilities [Line Items]
Available lines of credit	$ 40,000,000
Line of credit, borrowings outstanding	$ 0
Line Of Credit Facility Fixed Base Rate For Federal Funds	0.50%
Line Of Credit Facility Fixed Base Rate For Eurodollar Rate	1.00%
MGE [Member] \| MGE $40 million unsecured committed revolving line of credit \| Minimum [Member]
Credit Facilities [Line Items]
Line Of Credit Facility Floating Rate Based Adder	0.00%
Line Of Credit Facility Eurodollar Based Adder	0.625%
MGE [Member] \| MGE $40 million unsecured committed revolving line of credit \| Maximum [Member]
Credit Facilities [Line Items]
Line Of Credit Facility Floating Rate Based Adder	0.125%
Line Of Credit Facility Eurodollar Based Adder	1.125%
MGE Energy [Member] \| MGE Energy $50 million unsecured commiteed revolving line of credit
Credit Facilities [Line Items]
Available lines of credit	$ 50,000,000
Line of credit, borrowings outstanding	$ 0
Line Of Credit Facility Fixed Base Rate For Federal Funds	0.50%
Line Of Credit Facility Fixed Base Rate For Eurodollar Rate	1.00%
MGE Energy [Member] \| MGE Energy $50 million unsecured commiteed revolving line of credit \| Minimum [Member]
Credit Facilities [Line Items]
Line Of Credit Facility Floating Rate Based Adder	0.00%
Line Of Credit Facility Eurodollar Based Adder	0.625%
MGE Energy [Member] \| MGE Energy $50 million unsecured commiteed revolving line of credit \| Maximum [Member]
Credit Facilities [Line Items]
Line Of Credit Facility Floating Rate Based Adder	0.125%
Line Of Credit Facility Eurodollar Based Adder	1.125%

Borrowings under credit agreements may bear interest at a rate that floats daily based upon a Eurodollar rate.

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Borrowings under credit agreements may bear interest at a rate that floats daily based a Eurodollar rate for a one month interst period plus a fixed base rate.

+ References

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Borrowings under credit agreements may bear interest at a rate that floats daily based a federal funds effective rate plus a fixed base rate.

+ References

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Borrowings under credit agreements may bear interest at a rate that floats daily based on the highest of a prime rate, a federal funds effective rate plus 0.5% per annum, or a Eurodollar rate for a one month interest period plus 1%.

+ References

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- Definition

Carrying value as of the balance sheet date of short-term borrowings using unsecured obligations issued by banks, corporations and other borrowers to investors. The maturities of these money market securities generally do not exceed 270 days.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(a)(3))

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.13(2))

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 16

-Article 7

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Amount of increase (decrease) to net income used for calculating diluted earnings per share (EPS), resulting from the assumed exercise stock options, restrictive stock units (RSUs), convertible preferred stock of an employee stock ownership plan (ESOP), and other dilutive convertible securities.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 260

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

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- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.16)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.16)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 20, 22

-Article 5

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- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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- Definition

Number of new stock issued during the period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 50

-Paragraph 2

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-Subparagraph (SX 210.3-04)

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-Publisher SEC

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-Number 210

-Section 02

-Paragraph 29, 30

-Article 5

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