Schedule I - Condensed Parent Company Finanical Statements (Details-Cash Flow Statement) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Flows Provided by Operating Activities	$ 147,513	$ 141,185	$ 128,762
Investing Activities:
Other investing	(209)	(230)	(1,297)
Cash Used for Investing Activities	(86,826)	(73,313)	(96,158)
Financing Activities:
Cash dividends paid on common stock	(41,775)	(40,043)	(38,429)
Change in short-term debt	0	(7,000)	7,000
Other financing	(70)	(1,018)	(130)
Cash Used for Financing Activities	(46,112)	(52,243)	(35,662)
Change in cash and cash equivalents:	14,575	15,629	(3,058)
Cash and cash equivalents at beginning of period	81,384	65,755	68,813
Cash and cash equivalents at end of period	95,959	81,384	65,755
MGE Energy [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Flows Provided by Operating Activities	74,994	37,085	48,165
Investing Activities:
Other investing	(2,764)	(3,690)	(2,422)
Cash Used for Investing Activities	(2,764)	(3,690)	(2,422)
Financing Activities:
Cash dividends paid on common stock	(41,775)	(40,043)	(38,429)
Other financing	(11)	0	(89)
Cash Used for Financing Activities	(41,786)	(40,043)	(38,518)
Change in cash and cash equivalents:	30,444	(6,648)	7,225
Cash and cash equivalents at beginning of period	51,781	58,429	51,204
Cash and cash equivalents at end of period	$ 82,225	$ 51,781	$ 58,429