Pension Plans and Other Postretirement Benefits (Details-3) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Benefits [Member]
Weighted-average assumptions used to determine benefit obligations:
Discount rate	[1]	4.29%	4.51%
Rate of compensation increase		3.71%	3.78%
Weighted-average assumptions used to determine net periodic cost:
Discount rate		4.51%	4.11%	4.88%
Long-term rate of return		7.65%	7.80%	8.10%
Rate of compensation increase		3.76%	3.84%	3.93%
Postretirement Benefits [Member]
Weighted-average assumptions used to determine benefit obligations:
Discount rate	[1]	4.11%	4.32%
Assumed health care cost trend rates:
Health care cost trend rate assumed for next year		6.25%	6.50%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate)		5.00%	5.00%
Year that the rate reaches the ultimate trend rate		2022	2022
Weighted-average assumptions used to determine net periodic cost:
Discount rate		4.32%	3.96%	4.69%
Long-term rate of return		6.96%	7.06%	7.07%
How assumed 1% increase or decrease in health care cost trends could impact postretirement benefits [Abstract]
Effect on other postretirement benefit obligation - 1% increase		$ 1,175
Effect on other postretirement benefit obligation - 1% decrease		(1,479)
Effect on total service and interest cost components - 1% increase		54
Effect on total service and interest cost components - 1% decrease		$ (67)

[1] In 2015, MGE refined its methodology for using discount rates to measure the components of net periodic benefit cost. The refined methodology uses individual spot rates, instead of a weighted average of the yield curve spot rates, for measuring the service cost and interest cost components. The change in methodology does not alter the measurement of the related benefit obligation as of December 31, 2015.