Consolidated Balance Sheets - USD ($)		Dec. 31, 2020	Dec. 31, 2019
Current Assets:
Cash and cash equivalents		$ 44,738,000	$ 23,481,000
Accounts receivable, less reserves		41,384,000	40,482,000
Other accounts receivables, less reserves		7,300,000	7,940,000
Unbilled revenues		27,511,000	25,899,000
Materials and supplies, at average cost		32,513,000	26,287,000
Fuel for electric generation, at average cost		6,356,000	8,358,000
Stored natural gas, at average cost		8,396,000	10,637,000
Prepaid taxes		15,179,000	16,892,000
Regulatory assets - current		14,748,000	11,432,000
Other current assets		11,394,000	10,233,000
Total Current Assets		209,519,000	181,641,000
Other long-term receivables		1,435,000	1,811,000
Regulatory assets		142,504,000	134,314,000
Pension and other postretirement benefit asset		13,873,000	13,630,000
Other deferred assets and other		22,259,000	19,093,000
Property, Plant, and Equipment:
Property, plant, and equipment, net		1,630,286,000	1,530,199,000
Construction work in progress		139,099,000	112,484,000
Total Property, Plant, and Equipment		1,769,385,000	1,642,683,000
Investments		94,676,000	88,492,000
Total Assets		2,253,651,000	2,081,664,000
Current Liabilities:
Long-term debt due within one year		4,771,000	19,659,000
Short-term debt	[1]	52,500,000	0
Accounts payable		54,642,000	55,161,000
Accrued interest and taxes		8,539,000	7,244,000
Accrued payroll related items		12,635,000	12,752,000
Regulatory liabilities - current		41,664,000	9,228,000
Derivative liabilities		10,160,000	10,100,000
Other current liabilities		6,015,000	14,676,000
Total Current Liabilities		190,926,000	128,820,000
Other Credits:
Deferred income taxes		231,471,000	243,302,000
Investment tax credit - deferred		21,821,000	763,000
Regulatory liabilities		142,239,000	164,965,000
Accrued pension and other postretirement benefits		78,168,000	68,665,000
Derivative liabilities		3,980,000	15,340,000
Finance lease liabilities		17,532,000	17,379,000
Other deferred liabilities and other		72,211,000	63,013,000
Total Other Credits		567,422,000	573,427,000
Common shareholders' equity:
Common stock		36,163,000	34,668,000
Additional paid-in capital		394,408,000	316,268,000
Retained earnings		545,429,000	504,740,000
Total Common Shareholders' Equity		976,000,000	855,676,000
Long-term debt		519,303,000	523,741,000
Total Capitalization		1,495,303,000	1,379,417,000
Commitments and contingencies (see Footnote 16)
Total Liabilities and Capitalization		2,253,651,000	2,081,664,000
MGE [Member]
Current Assets:
Cash and cash equivalents		4,103,000	3,196,000
Accounts receivable, less reserves		41,384,000	40,482,000
Affiliate receivables		532,000	530,000
Other accounts receivables, less reserves		7,295,000	7,936,000
Unbilled revenues		27,511,000	25,899,000
Materials and supplies, at average cost		32,513,000	26,287,000
Fuel for electric generation, at average cost		6,356,000	8,358,000
Stored natural gas, at average cost		8,396,000	10,637,000
Prepaid taxes		14,848,000	15,463,000
Regulatory assets - current		14,748,000	11,432,000
Other current assets		11,326,000	10,065,000
Total Current Assets		169,012,000	160,285,000
Affiliate receivable long-term		2,118,000	2,648,000
Regulatory assets		142,504,000	134,314,000
Pension and other postretirement benefit asset		13,873,000	13,630,000
Other deferred assets and other		22,448,000	19,680,000
Property, Plant, and Equipment:
Property, plant, and equipment, net		1,630,314,000	1,530,227,000
Construction work in progress		139,099,000	112,484,000
Total Property, Plant, and Equipment		1,769,413,000	1,642,711,000
Investments		603,000	209,000
Total Assets		2,119,971,000	1,973,477,000
Current Liabilities:
Long-term debt due within one year		4,771,000	19,659,000
Short-term debt		52,500,000	0
Accounts payable		54,576,000	54,845,000
Accrued interest and taxes		10,405,000	8,754,000
Accrued payroll related items		12,635,000	12,752,000
Regulatory liabilities - current		41,664,000	9,228,000
Derivative liabilities		10,160,000	10,100,000
Other current liabilities		6,042,000	12,683,000
Total Current Liabilities		192,753,000	128,021,000
Other Credits:
Deferred income taxes		200,390,000	214,041,000
Investment tax credit - deferred		21,821,000	763,000
Regulatory liabilities		142,239,000	164,965,000
Accrued pension and other postretirement benefits		78,168,000	68,665,000
Derivative liabilities		3,980,000	15,340,000
Finance lease liabilities		17,532,000	17,379,000
Other deferred liabilities and other		72,173,000	62,973,000
Total Other Credits		536,303,000	544,126,000
Common shareholders' equity:
Common stock		17,348,000	17,348,000
Additional paid-in capital		252,917,000	222,917,000
Retained earnings		460,151,000	397,021,000
Total Common Shareholders' Equity		730,416,000	637,286,000
Noncontrolling interest		141,196,000	140,303,000
Total Equity		871,612,000	777,589,000
Long-term debt		519,303,000	523,741,000
Total Capitalization		1,390,915,000	1,301,330,000
Commitments and contingencies (see Footnote 16)
Total Liabilities and Capitalization		$ 2,119,971,000	$ 1,973,477,000

[1] MGE Energy short-term borrowings include MGE Energy and MGE lines of credit and MGE commercial paper.