Commitments and Contingencies (Details-1)	Sep. 30, 2017 USD ($)
Operating expense purchase contracts [Abstract]
Purchase obligation, 2017	$ 23,718,000
Purchase obligation, 2018	52,341,000
Purchase obligation, 2019	33,177,000
Purchase obligation, 2020	18,868,000
Purchase obligation, 2021	8,660,000
Purchase obligation, Thereafter	24,373,000
Coal [Member]
Operating expense purchase contracts [Abstract]
Purchase obligation, 2017	6,402,000	[1]
Purchase obligation, 2018	19,685,000	[1]
Purchase obligation, 2019	13,497,000	[1]
Purchase obligation, 2020	3,445,000	[1]
Purchase obligation, 2021	0	[1]
Purchase obligation, Thereafter	0	[1]
Natural Gas, Transportation and Storage [Member]
Operating expense purchase contracts [Abstract]
Purchase obligation, 2017	6,073,000	[2]
Purchase obligation, 2018	20,839,000	[2]
Purchase obligation, 2019	19,680,000	[2]
Purchase obligation, 2020	15,423,000	[2]
Purchase obligation, 2021	8,660,000	[2]
Purchase obligation, Thereafter	24,373,000	[2]
Natual Gas, Supply [Member]
Operating expense purchase contracts [Abstract]
Purchase obligation, 2017	11,243,000	[3]
Purchase obligation, 2018	11,817,000	[3]
Purchase obligation, 2019	0	[3]
Purchase obligation, 2020	0	[3]
Purchase obligation, 2021	0	[3]
Purchase obligation, Thereafter	0	[3]
MGE Energy [Member] | Investments in Non Public Entities, Capital Infusions [Member]
Other Commitments [Line Items]
Other commitment, initial agreed upon commitment total	$ 5,000,000

[1] Total coal commitments for the Columbia and Elm Road Units, including transportation. Fuel procurement for MGE's jointly owned Columbia and Elm Road Units is handled by WPL and WEPCO, respectively, who are the operators of those facilities.

[2] MGE's natural gas transportation and storage contracts require fixed monthly payments for firm supply pipeline transportation and storage capacity. The pricing components of the fixed monthly payments for the transportation and storage contracts are establ ished by FERC but may be subject to change .

[3] These commitments include market-based pricing.