Schedule I - Condensed Parent Company Finanical Statements (Details-Notes 2)	12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
MGE Energy [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	$ 27,714,000	$ 28,246,000	$ 26,735,000
First Mortgage Bonds [Member] | 7.70%, 2028 Series [Member]
Dividend Restrictions
Debt covenant, allowable amount available for payment of dividends	529,900,000
MGE [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	$ 0	0
Dividend Restrictions
Common equity ratio	0.602
MGE [Member] | Minimum [Member]
Dividend Restrictions
Dividend restrictions, common equity ratio	0.55
MGE Power Elm Road [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	$ 15,500,000	15,500,000	15,500,000
MGE Power West Campus [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	6,000,000	8,000,000	6,500,000
MGE Transco [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	5,864,000	4,653,000	4,625,000
MGEE Transco [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	350,000	93,000	60,000
NGV Fueling Services [Member]
Dividends from Affiliates [Line Items]
Dividends from affiliates	$ 0	$ 0	$ 50,000