Rate Matters (Details) - PSCW [Member] - MGE [Member] - USD ($)	1 Months Ended			4 Months Ended	12 Months Ended
	Oct. 31, 2018	Oct. 31, 2017	Sep. 30, 2016	Dec. 31, 2015	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Rate Proceedings [Abstract]
Approved equity capital structure, percentage								9.80%
Authorized return on equity, percentage								57.20%
Fuel Rules [Abstract]
Fuel rules, bandwidth							2.00%
Fuel rules, electric fuel costs, deferral, upper threshold							102.00%
Fuel rules, electric fuel costs, deferral, lower threshold							98.00%
Deferred fuel rules monitored costs							$ 9,500,000
Public Utilities Fuel Surcharge Amount							$ 500,000
Public Utilities Fuel Surcharge Percentage							0.13%
Fuel Rules Credit ($0.00256/kWh), 2015/2016 [Member]
Fuel Rules [Abstract]
Electric fuel credit (per kWh)				$ 0.00256					$ 0.00256
Return of electric fuel credit, total									$ 8,300,000
Fuel Rules Refund, 2015/2016 [Member]
Fuel Rules [Abstract]
Return of electric fuel credit, total		$ 6,200,000	$ 15,500,000
Fuel Rules Refund, 2017 [Member]
Fuel Rules [Abstract]
Return of electric fuel credit, total	$ 4,200,000
Approved Future Rate Matters [Member]
Rate Proceedings [Abstract]
Approved equity capital structure, percentage					9.80%	9.80%
Authorized return on equity, percentage					56.10%	56.60%
Electric Rate Proceeding [Member]
Rate Proceedings [Abstract]
Authorized rate increase (decrease), percentage								(0.80%)
Authorized rate increase (decrease), amount								$ (3,300,000)
Electric Rate Proceeding [Member] | Approved Future Rate Matters [Member]
Rate Proceedings [Abstract]
Authorized rate increase (decrease), percentage					0.00%	(2.24%)
Authorized rate increase (decrease), amount					$ 0	$ (9,200,000)
Gas Rate Proceeding [Member]
Rate Proceedings [Abstract]
Authorized rate increase (decrease), percentage								1.90%
Authorized rate increase (decrease), amount								$ 3,100,000
Gas Rate Proceeding [Member] | Approved Future Rate Matters [Member]
Rate Proceedings [Abstract]
Authorized rate increase (decrease), percentage					1.46%	1.06%
Authorized rate increase (decrease), amount					$ 2,400,000	$ 1,700,000