Variable Interest Entities (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Significant Balance Sheet Accounts Related to Interests in Variable Interest Entities
Property, plant, and equipment, net	$ 1,189,077,000		$ 1,018,809,000
Construction work in progress	19,029,000		141,415,000
Deferred income tax asset - current	3,482,000		0
Accrued interest and taxes	5,086,000		5,661,000
Other Variable Interest Entities
Other variable interest entities, purchase power agreement, plant capacity (in MW)	61		61
MGE Power Elm Road [Member]
Significant Balance Sheet Accounts Related to Interests in Variable Interest Entities
Property, plant, and equipment, net	179,620,000		182,657,000
Construction work in progress	1,976,000		1,115,000
Affiliate receivables, current and noncurrent	1,742,000		0
Deferred income tax asset - current	0		219,000
Deferred income taxes	40,044,000		34,141,000
Long-term debt, gross, current and noncurrent	67,972,000		70,639,000
Noncontrolling interest	72,537,000	[1]	69,876,000	[1]
Total carrying costs	62,500,000
Total capitalized interest	17,000,000
Total capitalized cost of equity	45,500,000
Carrying cost rate recovery period	6 years
MGE Power Elm Road [Member] | Minimum [Member]
Significant Balance Sheet Accounts Related to Interests in Variable Interest Entities
Debt service coverage ratio	1.25
MGE Power West Campus [Member]
Significant Balance Sheet Accounts Related to Interests in Variable Interest Entities
Property, plant, and equipment, net	86,763,000		89,564,000
Affiliate receivables, current and noncurrent	5,862,000		6,767,000
Accrued interest and taxes	569,000		4,888,000
Deferred income taxes	23,813,000		23,154,000
Long-term debt, gross, current and noncurrent	48,218,000		49,653,000
Noncontrolling interest	30,755,000	[1]	29,089,000	[1]
Carrying costs recovered	$ 12,100,000
Carrying cost rate recovery period	10 years
MGE Power West Campus [Member] | Minimum [Member]
Significant Balance Sheet Accounts Related to Interests in Variable Interest Entities
Debt service coverage ratio	1.25
MGE Power West Campus [Member] | Maximum [Member]
Significant Balance Sheet Accounts Related to Interests in Variable Interest Entities
Debt to total capitalization ratio	0.65

[1] MGE Power Elm Road and MGE Power West Campus are not subsidiaries of MGE; however, they have been consolidated in the consolidated financial statements of MGE (see Footnote 2). MGE Power Elm Road and MGE Power West Campus are100% owned by MGE Power, and MGE Power is 100% owned by MGE Energy. MGE Energy's proportionate share of the equity and net income (through its wholly owned subsidiary MGE Power) of MGE Power Elm Road and MGE Power West Campus is classified within the MGE financial statements as noncontrolling interest.