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Property, Plant, and Equipment (Details) (USD $) In Thousands, unless otherwise specified | Dec. 31, 2013 | Dec. 31, 2012
--- | --- | ---
Property, Plant and Equipment [Line Items] |  |  |  |
In-service utility plant, net | $ 1,018,809 |  | $ 975,053 |
Construction work in progress | 141,415 |  | 98,411 |
Total property, plant, and equipment | 1,160,224 |  | 1,073,464 |
First Mortgage Bonds [Member] | 7.70%, 2028 Series |  |  |  |
Plant related debt items |  |  |  |
Long-term debt, gross | 1,200 | [1] | 1,200 | [1]
Regulated [Member] |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
In-service utility plant, gross | 1,304,984 |  | 1,245,040 |
Less: Accumulated depreciation and amortization | 560,066 |  | 546,483 |
In-service utility plant, net | 744,918 |  | 698,557 |
Construction work in progress | 140,301 |  | 96,863 |
Electric [Member] | Regulated [Member] |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
In-service utility plant, gross | 953,290 |  | 912,273 |
Gas [Member] | Regulated [Member] |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
In-service utility plant, gross | 351,694 |  | 332,767 |
Non Regulated Energy [Member] | Non-regulated [Member] |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
In-service utility plant, gross | 311,742 |  | 308,043 |
Less: Accumulated depreciation and amortization | 37,851 |  | 31,547 |
In-service utility plant, net | 273,891 |  | 276,496 |
Construction work in progress | 1,114 |  | 1,548 |
MGE [Member] |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
In-service utility plant, net | 1,017,877 |  | 974,549 |
Construction work in progress | 141,415 |  | 98,411 |
Total property, plant, and equipment | 1,159,292 |  | 1,072,960 |
MGE [Member] | First Mortgage Bonds [Member] | 7.70%, 2028 Series |  |  |  |
Plant related debt items |  |  |  |
Long-term debt, gross | 1,200 | [1] | 1,200 | [1]
MGE [Member] | Regulated [Member] |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
In-service utility plant, gross | 1,305,012 |  | 1,245,068 |
Less: Accumulated depreciation and amortization | 560,066 |  | 546,483 |
In-service utility plant, net | 744,946 |  | 698,585 |
Construction work in progress | 140,301 |  | 96,863 |
MGE [Member] | Electric [Member] | Regulated [Member] |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
In-service utility plant, gross | 953,307 |  | 912,289 |
MGE [Member] | Gas [Member] | Regulated [Member] |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
In-service utility plant, gross | 351,705 |  | 332,779 |
MGE [Member] | Non Regulated Energy [Member] | Non-regulated [Member] |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |
In-service utility plant, gross | 310,745 |  | 307,511 |
Less: Accumulated depreciation and amortization | 37,814 |  | 31,547 |
In-service utility plant, net | 272,931 |  | 275,964 |
Construction work in progress | $ 1,114 |  | $ 1,548 |
[1] | MGE's utility plant is subject to the lien of its Indenture of Mortgage and Deed of Trust, under which its first mortgage bonds are issued. The Mortgage Indenture provides that dividends or any other distribution or purchase of shares may not be made if the aggregate amount thereof since December 31, 1945 would exceed the earned surplus (retained earnings) accumulated subsequent to December 31, 1945. As of December 31, 2013, approximately $305.6 million was available for the payment of dividends under this covenant.

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- Definition Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. This amount does not include Construction work in progress. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures. + References No definition available. + Details
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- Definition Amount, net of accumulated depreciation, depletion and amortization, of long-lived physical assets used in the normal conduct of business and not intended for resale. This amount does not include constrcution work in progress. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment. + References No definition available. + Details
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- Definition Gross amount, at the balance sheet date, of long-lived assets under construction that include construction costs to date on capital projects that have not been completed and assets being constructed that are not ready to be placed into service. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 5 -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 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 + Details
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