Property, Plant, and Equipment (Details) - USD ($) $ in Thousands		Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
In-service utility plant, net		$ 1,217,094	$ 1,189,077
Construction work in progress		26,351	19,029
Total property, plant, and equipment		1,243,445	1,208,106
First Mortgage Bonds [Member] | 7.70%, 2028 Series
Plant related debt items
Long-term debt, gross	[1]	1,200	1,200
Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		1,531,864	1,480,928
Less: Accumulated depreciation and amortization		578,410	559,615
In-service utility plant, net		953,454	921,313
Construction work in progress		23,837	16,988
Electric [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		1,147,701	1,110,953
Gas [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		384,163	369,975
Non Regulated Energy [Member] | Non-regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		315,589	313,152
Less: Accumulated depreciation and amortization		51,949	45,388
In-service utility plant, net		263,640	267,764
Construction work in progress		2,514	2,041
MGE [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, net		1,216,415	1,188,351
Construction work in progress		26,351	19,029
Total property, plant, and equipment		1,242,766	1,207,380
MGE [Member] | First Mortgage Bonds [Member] | 7.70%, 2028 Series
Plant related debt items
Long-term debt, gross	[1]	1,200	1,200
MGE [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		1,531,893	1,480,957
Less: Accumulated depreciation and amortization		578,410	559,615
In-service utility plant, net		953,483	921,342
Construction work in progress		23,837	16,988
MGE [Member] | Electric [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		1,147,718	1,110,970
MGE [Member] | Gas [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		384,175	369,987
MGE [Member] | Non Regulated Energy [Member] | Non-regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		314,750	312,314
Less: Accumulated depreciation and amortization		51,818	45,305
In-service utility plant, net		262,932	267,009
Construction work in progress		$ 2,514	$ 2,041

[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, 2015 , approximately $ 353.0 million was available for the payment of dividends under this covenant.