Schedule I - Condensed Parent Company Finanical Statements (Details-Cash Flow Statement) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Condensed Cash Flow Statements, Captions [Line Items]
Cash provided by operating activities	$ 172,443,000	$ 130,475,000	$ 153,040,000
Investing Activities:
Other	(1,672,000)	(508,000)	(205,000)
Cash Used for Investing Activities	(210,412,000)	(172,357,000)	(218,328,000)
Financing Activities:
Proceeds From Issuance Of Common Stock	79,635,000	0	0
Cash dividends paid on common stock	(51,729,000)	(47,842,000)	(45,762,000)
Other	(1,553,000)	(1,838,000)	(662,000)
Cash Provided by (Used for) Financing Activities	59,194,000	(17,233,000)	38,123,000
Change in cash, cash equivalents, and restricted cash:	21,225,000	(59,115,000)	(27,165,000)
Cash, cash equivalents, and restricted cash at beginning of period	25,814,000	84,929,000	112,094,000
Cash, cash equivalents, and restricted cash at end of period	47,039,000	25,814,000	84,929,000
MGE Energy [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Cash provided by operating activities	27,631,000	27,901,000	27,211,000
Investing Activities:
Contributions to affiliates	(32,157,000)	(33,631,000)	(3,200,000)
Contributions to other Investments	(3,809,000)	(4,496,000)	(2,626,000)
Other	622,000	214,000	873,000
Cash Used for Investing Activities	(35,344,000)	(37,913,000)	(4,953,000)
Financing Activities:
Proceeds From Issuance Of Common Stock	79,635,000	0	0
Cash dividends paid on common stock	(51,729,000)	(47,842,000)	(45,762,000)
Cash Provided by (Used for) Financing Activities	27,906,000	(47,842,000)	(45,762,000)
Change in cash, cash equivalents, and restricted cash:	20,193,000	(57,854,000)	(23,504,000)
Cash, cash equivalents, and restricted cash at beginning of period	17,182,000	75,036,000	98,540,000
Cash, cash equivalents, and restricted cash at end of period	$ 37,375,000	$ 17,182,000	$ 75,036,000