Noncontrolling Interest (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
MGE [Member]
Noncontrolling Interest [Line Items]
Noncontrolling interest on balance sheet		$ 115,665	$ 140,308
Net income attributable to noncontrolling interest, net of tax		23,358	26,097	$ 26,310
MGE Transco [Member]
Noncontrolling Interest [Line Items]
Noncontrolling interest on balance sheet	[1]	0	23,592
Net income attributable to noncontrolling interest, net of tax	[1]	$ 1,410	2,172	2,484
MGE Power [Member]
Noncontrolling Interest [Line Items]
Ownership percentage by parent		100.00%
MGE Power West Campus [Member]
Noncontrolling Interest [Line Items]
Ownership percentage by parent		100.00%
Noncontrolling interest on balance sheet	[2]	$ 35,303	37,603
Net income attributable to noncontrolling interest, net of tax	[2]	$ 7,200	7,348	7,666
MGE Power Elm Road [Member]
Noncontrolling Interest [Line Items]
Ownership percentage by parent		100.00%
Noncontrolling interest on balance sheet	[2]	$ 80,362	79,113
Net income attributable to noncontrolling interest, net of tax	[2]	$ 14,748	$ 16,577	$ 16,160

[1] At December 31, 2016 , MGE Energy is the owner of MGE Transco. In July 2016, MGE's ownership interest in MGE Transco declined bel ow a majority as a result of continued funding of ATC capital contributions by MGE Energy. As a result of the change in majority owner ship in MGE Transco , MGE deconsolidated MGE Energy's proportionate share of the equity in MGE Transco. The change in conso lidation was applied prospectively by reducing its investment and noncontrolling interest on MGE's consolidated financial statements. The change had no effect on MGE Energy's consolidated financial statements; however, MGE Energy's proportionate share of t he equity and net income of MGE Transco classified as noncontrolling interest was deconsolidated from MGE ' s financial statements. No gain or loss was recognized in July 2016 due to MGE ceasing to have a controlling financial interest .

[2] MGE Power Elm Road and MGE Power West Campus are not su bsidiaries of MGE; however, they have been consolidated in the consolidated financial statements of MGE (see Footnote 2). MGE Power Elm Road and MGE Power West Campus are 100 % owned by MGE Power, and MGE Power is 100 % o wned by MGE Energy. MGE Energy's proportionate share of the equity and net income (through its wholly owned subsidiary MGE Power) of MGE Power Elm Road and MGE Power West Campus is classified within the MGE consolidated financial statements as noncontrolling interest.