Investments (Details-2) (USD $) In Thousands, unless otherwise specified	12 Months Ended						1 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 MGE Transco [Member] ATC [Member]	Dec. 31, 2012 MGE Transco [Member] ATC [Member]	Dec. 31, 2011 MGE Transco [Member] ATC [Member]	Jan. 31, 2014 MGE Transco [Member] ATC [Member] Subsequent Event [Member]
Schedule Of Equity Method Investments [Line Items]
Equity in earnings in ATC	$ 9,434	$ 9,079	$ 8,615	$ 9,400	$ 9,100	$ 8,600
Dividend income from ATC	7,404	7,146	6,728	7,400	7,100	6,700
Contributions to investments	$ 1,660	$ 2,419	$ 1,008	$ 1,400	$ 2,100	$ 900	$ 500
MGE Transco ownership interest in ATC				3.60%	3.60%