Schedule I - Condensed Parent Company Finanical Statements (Details-Comprehensive Income Statement) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Expenses:
Other operations and maintenance									$ 161,703	$ 171,248	$ 172,996
Total Operating Expenses	116,141	95,015	104,324	166,274	129,301	100,199	103,791	129,609	481,754	462,900	428,560
Operating Income (Loss)	29,566	40,120	24,441	43,971	25,962	39,900	24,497	37,628	138,098	127,987	112,763
Equity in earnings of investments									9,150	9,434	9,079
Income before income taxes									128,504	119,764	103,365
Income tax provision	(8,600)	(14,286)	(9,034)	(16,265)	(7,829)	(14,692)	(8,660)	(13,678)	(48,185)	(44,859)	(38,919)
Net Income	15,186	23,329	14,087	27,717	14,077	24,353	13,891	22,584	80,319	74,905	64,446
Other comprehensive income/(loss), net of tax:
Unrealized gain (loss) on available for sale securities, net of tax									81	283	(18)
Comprehensive Income									80,400	75,188	64,428
MGE Energy [Member]
Operating Expenses:
Other operations and maintenance									689	613	649
Total Operating Expenses									689	613	649
Operating Income (Loss)									(689)	(613)	(649)
Equity in earnings of investments									81,811	76,362	65,132
Other income/(loss), net									(1,879)	(1,863)	(496)
Other interest									93	55	45
Income before income taxes									79,336	73,941	64,032
Income tax provision									983	964	414
Net Income									80,319	74,905	64,446
Other comprehensive income/(loss), net of tax:
Unrealized gain (loss) on available for sale securities, net of tax									81	283	(18)
Comprehensive Income									$ 80,400	$ 75,188	$ 64,428