Madison Gas and Electric Company Consolidated Statements of Common Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	MGE [Member]	Common Stock [Member]	Common Stock [Member] MGE [Member]	Additional Paid-In Capital [Member] MGE [Member]	Retained Earnings [Member] MGE [Member]	Accumulated Other Comprehensive Income/(Loss) [Member] MGE [Member]	Noncontrolling Interest [Member] MGE [Member]
Beginning balance, shares at Dec. 31, 2019			34,668	17,348
Beginning balance, value at Dec. 31, 2019		$ 777,589		$ 17,348	$ 222,917	$ 397,021	$ 0	$ 140,303
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income	$ 76,622	71,191				54,437		16,754
Capital contributions from parent		30,000			30,000
Distributions to parent from noncontrolling interest		(16,000)						(16,000)
Ending balance, shares at Sep. 30, 2020			36,163	17,348
Ending balance, value at Sep. 30, 2020		862,780		$ 17,348	252,917	451,458	0	141,057
Beginning balance, shares at Jun. 30, 2020			36,163	17,348
Beginning balance, value at Jun. 30, 2020		840,047		$ 17,348	252,917	426,718	0	143,064
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income	31,794	30,233				24,740		5,493
Distributions to parent from noncontrolling interest		(7,500)						(7,500)
Ending balance, shares at Sep. 30, 2020			36,163	17,348
Ending balance, value at Sep. 30, 2020		862,780		$ 17,348	252,917	451,458	0	141,057
Beginning balance, shares at Dec. 31, 2020			36,163	17,348
Beginning balance, value at Dec. 31, 2020		871,612		$ 17,348	252,917	460,151	0	141,196
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income	92,701	87,529				70,774		16,755
Capital contributions from parent		0
Distributions to parent from noncontrolling interest		(10,500)						(10,500)
Ending balance, shares at Sep. 30, 2021			36,163	17,348
Ending balance, value at Sep. 30, 2021		948,641		$ 17,348	252,917	530,925	0	147,451
Beginning balance, shares at Jun. 30, 2021			36,163	17,348
Beginning balance, value at Jun. 30, 2021		918,640		$ 17,348	252,917	503,551	0	144,824
Increase (Decrease) In Stockholders' Equity [Roll Forward]
Net Income	$ 34,917	33,001				27,374		5,627
Distributions to parent from noncontrolling interest		(3,000)						(3,000)
Ending balance, shares at Sep. 30, 2021			36,163	17,348
Ending balance, value at Sep. 30, 2021		$ 948,641		$ 17,348	$ 252,917	$ 530,925	$ 0	$ 147,451