Elm Road (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2011
Elm Road Units [Member] | MGE Power Elm Road [Member]
Elm Road Units ownership [Line Items]
Ownership interest in jointly owned plant	8.33%
Plant capacity - MW	615
Elm Road Units [Member]
Elm Road [Line Items]
Elm Road placed in-service	$ 195.8
Total carrying costs	62.2
Total capitalized interest	17.0
Total capitalized cost of equity	45.2
Total carrying costs recoverable during the year	4.8
Carrying costs collected during the year	3.6
Capitalized interest collected in rates during the year	0.7
Capitalized cost of equity collected in rates during the year	$ 2.9