Property, Plant, and Equipment (Details)		12 Months Ended
		Dec. 31, 2019 USD ($) Turbines MW	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Property, Plant and Equipment [Line Items]
In-service utility plant, net		$ 1,530,199,000	$ 1,369,766,000
Construction work in progress		112,484,000	139,671,000
Total property, plant, and equipment		1,642,683,000	1,509,437,000
Assets Held For Sale
Assets held for sale		0	3,080,000
Allowance for Funds Used During Construction
AFUDC equity recognized		$ 2,300,000	$ 3,300,000	$ 1,200,000
PSCW [Member]
Allowance for Funds Used During Construction
Authorized AFUDC rate		50.00%	50.00%	50.00%
Authorized AFUDC rate - Signficiant projects (100%)		100.00%	100.00%	100.00%
Saratoga Wind [Member]
Saratoga Wind [Abstract]
Saratoga Megawatts | MW		66
Saratoga Turbines | Turbines		33
Saratoga Wind Project Costs		$ 107,900,000
Allowance for Funds Used During Construction
AFUDC equity recognized		$ 4,100,000
Saratoga Wind [Member] | PSCW [Member]
Allowance for Funds Used During Construction
Authorized AFUDC rate - Signficiant projects (100%)		100.00%
First Mortgage Bonds [Member] | 7.70%, 2028 Series
Plant related debt items
Long-term debt, gross	[1]	$ 1,200,000	$ 1,200,000
Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		1,952,807,000	1,753,002,000
Less: Accumulated depreciation and amortization	[2]	674,251,000	639,486,000
In-service utility plant, net		1,278,556,000	1,113,516,000
Construction work in progress	[2],[3],[4]	111,707,000	138,663,000
Electric [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross	[2],[4]	1,480,684,000	1,310,421,000
Gas [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		472,123,000	442,581,000
Non Regulated Energy [Member] | Non-regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		323,266,000	322,855,000
Less: Accumulated depreciation and amortization		71,623,000	66,605,000
In-service utility plant, net		251,643,000	256,250,000
Construction work in progress		777,000	1,008,000
MGE [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, net		1,530,227,000	1,369,795,000
Construction work in progress		112,484,000	139,671,000
Total property, plant, and equipment		1,642,711,000	1,509,466,000
Assets Held For Sale
Assets held for sale		0	3,080,000
MGE [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		1,952,835,000	1,753,031,000
Less: Accumulated depreciation and amortization	[2]	674,251,000	639,486,000
In-service utility plant, net		1,278,584,000	1,113,545,000
Construction work in progress	[2],[3],[4]	111,707,000	138,663,000
MGE [Member] | Electric [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross	[2],[4]	1,480,701,000	1,310,438,000
MGE [Member] | Gas [Member] | Regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		472,134,000	442,593,000
MGE [Member] | Non Regulated Energy [Member] | Non-regulated [Member]
Property, Plant and Equipment [Line Items]
In-service utility plant, gross		323,266,000	322,855,000
Less: Accumulated depreciation and amortization		71,623,000	66,605,000
In-service utility plant, net		251,643,000	256,250,000
Construction work in progress		$ 777,000	$ 1,008,000

[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 MGE 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, 2019, approximately $465.2 million was available for the payment of dividends under this covenant.

[2] As of December 31, 2018, MGE has classified $3.1 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 6.a. for further discussion.

[3] 2019 includes construction expenditures for Badger Hollow I and Two Creeks. See Footnote 6 for further information.

[4] In December 2017, the PSCW authorized construction of a 66 MW wind farm, consisting of 33 turbines, located near Saratoga, Iowa. The project was placed in service in February 2019. Total capitalized expenditures of the project were $107.9 million,including $4.1 million of AFUDC. MGE received specific approval to recover 100% AFUDC on the project.