Commitments and Contingencies (Details-4)	12 Months Ended
	Dec. 31, 2017 USD ($)
Investments in Non Public Entities, Capital Infusions [Member] | MGE Energy [Member]
Other Commitments [Line Items]
Other commitment, initial agreed upon commitment total	$ 11,100,000
Venture Debt Fund [Member] | MGE Energy [Member]
Other Commitments [Line Items]
Other commitment, contract term, expiring in 2019	3 years
Other commitment, initial agreed upon commitment total	$ 1,500,000
Other commitments, total as of balance sheet date	400,000
MGE [Member]
Other Commitments [Line Items]
Other commitments, due in 2018	435,000
Other commitments, due in 2019	437,000
Other commitments, due in 2020	438,000
Other commitments, due in 2021	441,000
Other commitments, due in 2022	442,000
Other commitment, due thereafter	$ 5,202,000