Joint Plant Ownership (Details) (USD $)	12 Months Ended
	Dec. 31, 2011 MW	Dec. 31, 2010	Dec. 31, 2009
Columbia Units [Member]
Jointly Owned Plants [Line Items]
Generating capability - MW	225
Jointly owned plant's share of MGE's net generating capability	29.00%
Ownership interest in jointly owned plant	22.00%
MGE's share of fuel, operating, and maintenance expenses	$ 37,100,000	$ 35,900,000	$ 30,100,000
Jointly Owned Plants Net Plant Ownership [Abstract]
Plant	118,227,000	114,760,000
Accumulated depreciation	(76,371,000)	(73,771,000)
Property, plant, and equipment, net	41,856,000	40,989,000
Elm Road Units [Member]
Jointly Owned Plants [Line Items]
MGE's share of fuel, operating, and maintenance expenses	18,000,000	7,400,000
Elm Road Units [Member] | MGE Power Elm Road [Member]
Jointly Owned Plants [Line Items]
Generating capability - MW	615
Ownership interest in jointly owned plant	8.33%
Jointly Owned Plants Net Plant Ownership [Abstract]
Plant	195,926,000	122,603,000
Accumulated depreciation	(6,763,000)	(2,481,000)
Property, plant, and equipment, net	189,163,000	120,122,000
Construction work in progress	732,000	72,193,000
Total property, plant, and equipment	189,895,000	192,315,000
West Campus [Member]
Jointly Owned Plants [Line Items]
UW's ownership interest in jointly owned plant	45.00%
UW's share of fuel, operating, and maintenance expenses	5,000,000	4,000,000	2,600,000
West Campus [Member] | MGE Power West Campus [Member]
Jointly Owned Plants [Line Items]
Ownership interest in jointly owned plant	55.00%
Jointly Owned Plants Net Plant Ownership [Abstract]
Plant	109,620,000	109,152,000
Accumulated depreciation	(18,265,000)	(15,521,000)
Property, plant, and equipment, net	$ 91,355,000	$ 93,631,000