Schedule I - Condensed Parent Company Finanical Statements (Details-Cash Flow Statement) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Cash Flow Statements, Captions [Line Items]
Cash provided by operating activities	$ 130,475,000	$ 153,040,000	$ 131,373,000
Investing Activities:
Other	(508,000)	(205,000)	118,000
Cash Used for Investing Activities	(172,357,000)	(218,328,000)	(116,275,000)
Financing Activities:
Cash dividends paid on common stock	(47,842,000)	(45,762,000)	(43,682,000)
Other	(1,838,000)	(662,000)	(597,000)
Cash Provided by (Used for) Financing Activities	(17,233,000)	38,123,000	(4,637,000)
Change in cash, cash equivalents, and restricted cash:	(59,115,000)	(27,165,000)	10,461,000
Cash, cash equivalents, and restricted cash at beginning of period	84,929,000	112,094,000	101,633,000
Cash, cash equivalents, and restricted cash at end of period	25,814,000	84,929,000	112,094,000
MGE Energy [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Cash provided by operating activities	27,901,000	27,211,000	70,268,000
Investing Activities:
Contributions to affiliates	(33,631,000)	(3,200,000)	(6,522,000)
Contributions to other Investments	(4,496,000)	(2,626,000)	(4,534,000)
Other	214,000	873,000	843,000
Cash Used for Investing Activities	(37,913,000)	(4,953,000)	(10,213,000)
Financing Activities:
Cash dividends paid on common stock	(47,842,000)	(45,762,000)	(43,682,000)
Other	0	0	(58,000)
Cash Provided by (Used for) Financing Activities	(47,842,000)	(45,762,000)	(43,740,000)
Change in cash, cash equivalents, and restricted cash:	(57,854,000)	(23,504,000)	16,315,000
Cash, cash equivalents, and restricted cash at beginning of period	75,036,000	98,540,000	82,225,000
Cash, cash equivalents, and restricted cash at end of period	$ 17,182,000	$ 75,036,000	$ 98,540,000