Joint Plant Ownership (Details) (USD $)	12 Months Ended
	Dec. 31, 2013 MW	Dec. 31, 2012	Dec. 31, 2011
Columbia Units [Member]
Jointly Owned Plants, Net Plant Ownership [Abstract]
Plant	$ 123,097,000	$ 119,544,000
Accumulated depreciation	(78,880,000)	(78,016,000)
Property, plant, and equipment, net	44,217,000	41,528,000
Construction work in progress	120,858,000	59,917,000
Total property, plant, and equipment	165,075,000	101,445,000
Columbia Units [Member] | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, proportion of total net summer generating capability	31.00%
Jointly owned utility plant, plant capacity (in MW)	245
Jointly owned utility plant, ownership interest	22.00%
Jointly owned utility plant, fuel, operating, and maintenance expense	37,500,000	36,300,000	37,100,000
Elm Road Units [Member] | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, fuel, operating, and maintenance expense	13,400,000	13,200,000	18,000,000
Elm Road Units [Member] | MGE Power Elm Road [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, proportion of total net summer generating capability	14.00%
Jointly owned utility plant, plant capacity (in MW)	106
Jointly owned utility plant, number of operating units	2
Jointly Owned Plants, Net Plant Ownership [Abstract]
Plant	198,198,000	196,146,000
Accumulated depreciation	(15,541,000)	(11,126,000)
Property, plant, and equipment, net	182,657,000	185,020,000
Construction work in progress	1,115,000	1,440,000
Total property, plant, and equipment	183,772,000	186,460,000
Elm Road Unit 1 [Member] | MGE Power Elm Road [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, plant capacity (in MW)	615
Jointly owned utility plant, ownership interest	8.33%
Elm Road Unit 2 [Member] | MGE Power Elm Road [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, plant capacity (in MW)	615
Jointly owned utility plant, ownership interest	8.33%
West Campus [Member] | UW [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, ownership interest	45.00%
Jointly owned utility plant, fuel, operating, and maintenance expense	4,900,000	4,900,000	5,000,000
West Campus [Member] | MGE Power West Campus [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, ownership interest	55.00%
Jointly Owned Plants, Net Plant Ownership [Abstract]
Plant	111,268,000	110,266,000
Accumulated depreciation	(21,704,000)	(19,927,000)
Property, plant, and equipment, net	$ 89,564,000	$ 90,339,000