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.