Rate Matters (Details) - PSCW [Member] - MGE [Member] - USD ($)	1 Months Ended		4 Months Ended	12 Months Ended
	Oct. 31, 2017	Sep. 30, 2016	Dec. 31, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Rate Proceedings [Abstract]
Approved equity capital structure, percentage					57.20%
Authorized return on equity, percentage					9.80%		10.20%
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					$ 4,200,000
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			$ 2,600,000			$ 8,300,000
Fuel Rules Refund, 2015/2016 [Member]
Fuel Rules [Abstract]
Return of electric fuel credit, total	$ 6,200,000	$ 15,500,000
Approved Future Rate Matters [Member]
Fuel Rules [Abstract]
Public Utilities Fuel Surcharge Amount				$ 500,000
Public Utilities Fuel Surcharge Percentage				0.13%
Electric Rate Proceeding [Member]
Rate Proceedings [Abstract]
Authorized rate increase (decrease), percentage					(0.80%)	0.00%	3.80%
Authorized rate increase (decrease), amount					$ (3,300,000)	$ 0	$ 15,400,000
Gas Rate Proceeding [Member]
Rate Proceedings [Abstract]
Authorized rate increase (decrease), percentage					1.90%	0.00%	(2.00%)
Authorized rate increase (decrease), amount					$ 3,100,000	$ 0	$ (3,800,000)