Variable Interest Entities (Details) $ in Thousands		Dec. 31, 2021 USD ($) MW	Dec. 31, 2020 USD ($) MW
Variable Interest Entity [Line Items]
In-service utility plant, net		$ 1,828,171	$ 1,630,286
Construction work in progress		50,603	139,099
Accrued interest and accrued (prepaid) taxes		10,385	8,539
Deferred income taxes		231,149	231,471
Unamortized discount and debt issuance costs		$ 4,349	$ 4,146
Other Variable Interest Entities
Other variable interest entities, purchase power agreement, plant capacity (in MW) | MW		13	13
MGE Power Elm Road [Member]
Variable Interest Entity [Line Items]
In-service utility plant, net		$ 163,325	$ 166,883
Construction work in progress		898	697
Affiliate receivables, current and noncurrent		0	0
Accrued interest and accrued (prepaid) taxes		37	2,701
Deferred income taxes		30,696	30,646
Long-term debt	[1]	48,968	51,590
Noncontrolling interest		101,507	96,856
Unamortized discount and debt issuance costs		300	400
MGE Power West Campus [Member]
Variable Interest Entity [Line Items]
In-service utility plant, net		79,183	79,077
Construction work in progress		493	677
Affiliate receivables, current and noncurrent		2,211	2,803
Accrued interest and accrued (prepaid) taxes		75	671
Deferred income taxes		14,726	14,521
Long-term debt	[1]	35,563	37,652
Noncontrolling interest		47,080	44,340
Unamortized discount and debt issuance costs		$ 100	$ 100

[1] MGE Power Elm Road's long-term debt includes debt issuance costs of $0.3 million and $0.4 million as of December 31, 2021 and 2020, respectively. The debt is secured by a collateral assignment of lease payments that MGE makes to MGE Power Elm Road for use of the Elm Road Units pursuant to the related long-term leases. MGE Power West Campus's long-term debt includes debt issuance costs of $0.1 million as of December 31, 2021 and 2020. The debt is secured by a collateral assignment of lease payments that MGE makes to MGE Power West Campus for use of the cogeneration facility pursuant to the long-term lease. See Footnote 14 for further information on the long-term debt securities