Property, Plant, and Equipment (Details) - USD ($) $ in Thousands		Dec. 31, 2016		Dec. 31, 2015
Property, Plant and Equipment [Line Items]
In-service utility plant, net		$ 1,245,269		$ 1,217,094
Construction work in progress		36,790		26,351
Total property, plant, and equipment		1,282,059		1,243,445
Assets held for sale		14,813		0
Plant related debt items
Long-term debt, gross		391,242
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		1,566,794		1,531,864
Less: Accumulated depreciation and amortization		579,965	[2]	578,410
In-service utility plant, net		986,829		953,454
Construction work in progress		31,356	[2]	23,837
Electric [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		1,171,004	[2]	1,147,701
Gas [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		395,790		384,163
Non Regulated Energy [Member] | Non-regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		317,810		315,589
Less: Accumulated depreciation and amortization		59,370		51,949
In-service utility plant, net		258,440		263,640
Construction work in progress		5,434		2,514
MGE [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, net		1,244,648		1,216,415
Construction work in progress		36,790		26,351
Total property, plant, and equipment		1,281,438		1,242,766
Assets held for sale		14,813		0
Plant related debt items
Long-term debt, gross	[3]	391,242
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		1,566,822		1,531,893
Less: Accumulated depreciation and amortization		579,965	[2]	578,410
In-service utility plant, net		986,857		953,483
Construction work in progress		31,356	[2]	23,837
MGE [Member] | Electric [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		1,171,021	[2]	1,147,718
MGE [Member] | Gas [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		395,801		384,175
MGE [Member] | Non Regulated Energy [Member] | Non-regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		317,014		314,750
Less: Accumulated depreciation and amortization		59,223		51,818
In-service utility plant, net		257,791		262,932
Construction work in progress		$ 5,434		$ 2,514

[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, 2016 , approximately $ 338.5 m illion was available for the payment of dividends under this covenant.

[2] As of December 31, 2016 , MGE has classified $ 14.8 million of Columbia assets as held-for-sale on the consolidated balance sheets related to the partial sale of plant assets to WPL . See Footnote 5.a. for further discussion.

[3] *Includes $ 45.1 million for MGE Power West Campus and $ 62.6 million for MGE Power Elm Road, all of which are consolidated wi th MGE's debt (see Footnote 2 for further information) .