Schedule I - Condensed Parent Company Finanical Statements (Details-Cash Flow Statement) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Cash Flow Statements, Captions [Line Items]
Cash provided by operating activities	$ 153,040	$ 131,373	$ 147,864
Investing Activities:
Other	(205)	118	(196)
Cash Used for Investing Activities	(218,328)	(116,275)	(86,813)
Financing Activities:
Cash dividends paid on common stock	(45,762)	(43,682)	(41,775)
Other	(662)	(597)	(70)
Cash Provided by (Used for) Financing Activities	38,123	(4,637)	(46,112)
Change in cash, cash equivalents, and restricted cash:	(27,165)	10,461	14,939
Cash, cash equivalents, and restricted cash at beginning of period	112,094	101,633	86,694
Cash, cash equivalents, and restricted cash at end of period	84,929	112,094	101,633
MGE Energy [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Cash provided by operating activities	27,211	70,268	74,994
Investing Activities:
Contributions to affiliates	(3,200)	(6,522)	(2,789)
Contributions to other Investments	(2,626)	(4,534)	(360)
Other	873	843	385
Cash Used for Investing Activities	(4,953)	(10,213)	(2,764)
Financing Activities:
Cash dividends paid on common stock	(45,762)	(43,682)	(41,775)
Other	0	(58)	(11)
Cash Provided by (Used for) Financing Activities	(45,762)	(43,740)	(41,786)
Change in cash, cash equivalents, and restricted cash:	(23,504)	16,315	30,444
Cash, cash equivalents, and restricted cash at beginning of period	98,540	82,225	51,781
Cash, cash equivalents, and restricted cash at end of period	$ 75,036	$ 98,540	$ 82,225