Joint Plant Ownership (Details) - MGE [Member]	Sep. 30, 2019 USD ($) MW
Two Creeks Units [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, ownership interest	33.00%
Jointly owned utility plant, plant capacity (in MW) | MW	150
Projected Solar Farm Project Costs	$ 65,000,000
Public Utilities Property Plant And Equipment Construction Work In Progress	$ 42,100,000
Badger Hollow Units [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, ownership interest	33.00%
Jointly owned utility plant, plant capacity (in MW) | MW	150
Projected Solar Farm Project Costs	$ 65,000,000
Public Utilities Property Plant And Equipment Construction Work In Progress	$ 10,000,000.0