Consolidated Balance Sheets - USD ($)		Dec. 31, 2018	Dec. 31, 2017
Current Assets:
Cash and cash equivalents		$ 83,102,000	$ 107,952,000
Accounts receivable, less reserves		43,593,000	42,299,000
Other accounts receivables, less reserves		6,262,000	9,440,000
Unbilled revenues		28,243,000	31,400,000
Materials and supplies, at average cost		24,093,000	22,614,000
Fuel for electric generation, at average cost		6,599,000	8,256,000
Stored natural gas, at average cost		11,303,000	12,923,000
Prepaid taxes		16,215,000	26,535,000
Regulatory assets - current		9,477,000	7,888,000
Assets held for sale		3,080,000	8,817,000
Other current assets		8,593,000	12,507,000
Total Current Assets		240,560,000	290,631,000
Other long-term receivables		2,709,000	4,788,000
Regulatory assets		145,424,000	142,567,000
Pension and other postretirement benefit asset		0	7,336,000
Other deferred assets and other		12,488,000	731,000
Property, Plant, and Equipment:
Property, plant, and equipment, net		1,369,766,000	1,283,313,000
Construction work in progress		139,671,000	58,044,000
Total Property, Plant, and Equipment		1,509,437,000	1,341,357,000
Investments		78,000,000	67,772,000
Total Assets		1,988,618,000	1,855,182,000
Current Liabilities:
Long-term debt due within one year		4,553,000	24,452,000
Short-term debt	[1]	13,000,000	4,000,000
Accounts payable		46,158,000	47,645,000
Accrued interest and taxes		7,384,000	5,602,000
Accrued payroll related items		13,044,000	12,244,000
Regulatory liabilities - current		13,826,000	5,633,000
Derivative liabilities		8,550,000	8,180,000
Other current liabilities		14,113,000	18,758,000
Total Current Liabilities		120,628,000	126,514,000
Other Credits:
Deferred income taxes		231,952,000	225,130,000
Investment tax credit - deferred		818,000	918,000
Regulatory liabilities		165,638,000	154,153,000
Accrued pension and other postretirement benefits		67,483,000	69,088,000
Derivative liabilities		23,980,000	33,990,000
Other deferred liabilities and other		68,132,000	69,041,000
Total Other Credits		558,003,000	552,320,000
Common shareholders' equity:
Common stock		34,668,000	34,668,000
Additional paid-in capital		316,268,000	316,268,000
Retained earnings		465,708,000	426,874,000
Accumulated other comprehensive income, net of tax		0	377,000
Total Common Shareholders' Equity		816,644,000	778,187,000
Long-term debt		493,343,000	398,161,000
Total Capitalization		1,309,987,000	1,176,348,000
Commitments and contingencies (see Footnote 17)
Total Liabilities and Capitalization		1,988,618,000	1,855,182,000
MGE [Member]
Current Assets:
Cash and cash equivalents		4,843,000	5,951,000
Accounts receivable, less reserves		43,593,000	42,299,000
Affiliate receivables		621,000	668,000
Other accounts receivables, less reserves		6,111,000	6,984,000
Unbilled revenues		28,243,000	31,400,000
Materials and supplies, at average cost		24,093,000	22,614,000
Fuel for electric generation, at average cost		6,599,000	8,256,000
Stored natural gas, at average cost		11,303,000	12,923,000
Prepaid taxes		15,790,000	25,073,000
Regulatory assets - current		9,477,000	7,888,000
Assets held for sale		3,080,000	8,817,000
Other current assets		8,541,000	12,484,000
Total Current Assets		162,294,000	185,357,000
Affiliate receivable long-term		3,177,000	3,707,000
Regulatory assets		145,424,000	142,567,000
Pension and other postretirement benefit asset		0	7,336,000
Other deferred assets and other		14,142,000	3,280,000
Property, Plant, and Equipment:
Property, plant, and equipment, net		1,369,795,000	1,283,341,000
Construction work in progress		139,671,000	58,044,000
Total Property, Plant, and Equipment		1,509,466,000	1,341,385,000
Investments		388,000	409,000
Total Assets		1,834,891,000	1,684,041,000
Current Liabilities:
Long-term debt due within one year		4,553,000	24,452,000
Short-term debt		13,000,000	4,000,000
Accounts payable		46,165,000	47,614,000
Accrued interest and taxes		10,319,000	5,558,000
Accrued payroll related items		13,044,000	12,244,000
Regulatory liabilities - current		13,826,000	5,633,000
Derivative liabilities		8,550,000	8,180,000
Other current liabilities		11,614,000	16,749,000
Total Current Liabilities		121,071,000	124,430,000
Other Credits:
Deferred income taxes		204,616,000	201,486,000
Investment tax credit - deferred		818,000	918,000
Regulatory liabilities		165,638,000	154,153,000
Accrued pension and other postretirement benefits		67,483,000	69,088,000
Derivative liabilities		23,980,000	33,990,000
Other deferred liabilities and other		68,132,000	69,041,000
Total Other Credits		530,667,000	528,676,000
Common shareholders' equity:
Common stock		17,348,000	17,348,000
Additional paid-in capital		192,417,000	192,417,000
Retained earnings		338,591,000	282,135,000
Accumulated other comprehensive income, net of tax		0	(28,000)
Total Common Shareholders' Equity		548,356,000	491,872,000
Noncontrolling interest		141,454,000	140,902,000
Total Equity		689,810,000	632,774,000
Long-term debt		493,343,000	398,161,000
Total Capitalization		1,183,153,000	1,030,935,000
Commitments and contingencies (see Footnote 17)
Total Liabilities and Capitalization		$ 1,834,891,000	$ 1,684,041,000

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