Joint Plant Ownership (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) operatingunit MW	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Columbia Units [Member]
Jointly Owned Plants, Net Plant Ownership [Abstract]
Plant	$ 273,762	$ 268,597
Accumulated depreciation	(84,864)	(80,645)
Property, plant, and equipment, net	188,898	187,952
Construction work in progress	17,110	6,941
Total property, plant, and equipment	$ 206,008	194,893
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) | MW	242
Jointly owned utility plant, ownership interest	22.00%
Jointly owned utility plant, fuel, operating, and maintenance expense	$ 38,200	28,100	$ 37,500
Elm Road Units [Member] | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, fuel, operating, and maintenance expense	$ 20,900	20,300	13,400
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, proportion of total net summer generating capability, plant capacity (in MW) | MW	106
Jointly owned utility plant, number of operating units | operatingunit	2
Jointly Owned Plants, Net Plant Ownership [Abstract]
Plant	$ 202,326	199,582
Accumulated depreciation	(24,422)	(19,962)
Property, plant, and equipment, net	177,904	179,620
Construction work in progress	2,400	1,976
Total property, plant, and equipment	$ 180,304	181,596
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) | 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) | 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	$ 3,700	2,800	$ 4,900
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	$ 111,141	111,453
Accumulated depreciation	(26,738)	(24,691)
Property, plant, and equipment, net	$ 84,403	$ 86,762