Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Activities:
Net Income	$ 92,418,000	$ 86,874,000	$ 84,219,000
Items not affecting cash:
Depreciation and amortization	74,188,000	71,562,000	56,412,000
Deferred income taxes	10,363,000	7,212,000	3,749,000
Provision for doubtful receivables	1,415,000	1,615,000	1,366,000
Employee benefit plan (credit) cost	(3,716,000)	(3,813,000)	(2,002,000)
Equity earnings in investments	(10,221,000)	(9,889,000)	(8,821,000)
Other items	(2,750,000)	163,000	(814,000)
Changes in working capital items:
Trade and other receivables (change)	(3,838,000)	(1,285,000)	(2,235,000)
Inventories (change)	(842,000)	(3,420,000)	2,724,000
Unbilled revenues (change)	(1,613,000)	2,345,000	3,157,000
Prepaid taxes (change)	1,713,000	(677,000)	10,320,000
Other current assets (change)	(1,057,000)	29,000	251,000
Accounts payable (change)	14,353,000	(7,432,000)	(4,855,000)
Other current liabilities (change)	(5,635,000)	(10,264,000)	11,957,000
Dividends from investment	8,998,000	7,347,000	6,958,000
Cash contributions to pension and other postretirement plans	(6,296,000)	(5,714,000)	(5,584,000)
Other noncurrent items, net	4,963,000	(4,178,000)	(3,762,000)
Cash Provided by Operating Activities	172,443,000	130,475,000	153,040,000
Investing Activities:
Capital expenditures	(203,139,000)	(164,036,000)	(212,197,000)
Capital contributions to investments	(5,601,000)	(7,813,000)	(5,926,000)
Other	(1,672,000)	(508,000)	(205,000)
Cash Used for Investing Activities	(210,412,000)	(172,357,000)	(218,328,000)
Financing Activities:
Issuance of common stock, net	79,635,000	0	0
Cash dividends paid on common stock	(51,729,000)	(47,842,000)	(45,762,000)
Repayment of long-term debt	(38,959,000)	(4,553,000)	(24,453,000)
Issuance of long-term debt	19,300,000	50,000,000	100,000,000
Proceeds from (Repayments of) short-term debt	52,500,000	(13,000,000)	9,000,000
Other	(1,553,000)	(1,838,000)	(662,000)
Cash Provided by (Used for) Financing Activities	59,194,000	(17,233,000)	38,123,000
Change in cash, cash equivalents, and restricted cash:	21,225,000	(59,115,000)	(27,165,000)
Cash, cash equivalents, and restricted cash at beginning of period	25,814,000	84,929,000	112,094,000
Cash, cash equivalents, and restricted cash at end of period	47,039,000	25,814,000	84,929,000
Supplemental disclosures of cash flow information:
Interest paid	23,898,000	23,171,000	20,018,000
Income taxes paid	8,127,000	14,617,000	12,597,000
Income taxes received	0	(255,000)	(59,000)
Significant noncash investing activities:
Accrued capital expenditures	5,719,000	26,697,000	11,129,000
MGE [Member]
Operating Activities:
Net Income	85,523,000	80,779,000	79,036,000
Items not affecting cash:
Depreciation and amortization	74,188,000	71,562,000	56,412,000
Deferred income taxes	8,543,000	5,286,000	(69,000)
Provision for doubtful receivables	1,415,000	1,615,000	1,366,000
Employee benefit plan (credit) cost	(3,716,000)	(3,813,000)	(2,002,000)
Other items	(1,828,000)	1,256,000	(107,000)
Changes in working capital items:
Trade and other receivables (change)	(3,840,000)	(1,285,000)	(2,160,000)
Inventories (change)	(842,000)	(3,420,000)	2,724,000
Unbilled revenues (change)	(1,613,000)	2,345,000	3,157,000
Prepaid taxes (change)	616,000	327,000	9,283,000
Other current assets (change)	(1,157,000)	147,000	255,000
Accounts payable (change)	14,603,000	(7,754,000)	(4,817,000)
Accrued interest and taxes (change)	1,651,000	(1,565,000)	4,761,000
Other current liabilities (change)	(4,909,000)	(9,618,000)	9,685,000
Cash contributions to pension and other postretirement plans	(6,296,000)	(5,714,000)	(5,584,000)
Other noncurrent items, net	3,980,000	(4,278,000)	(3,946,000)
Cash Provided by Operating Activities	166,318,000	125,870,000	147,994,000
Investing Activities:
Capital expenditures	(203,139,000)	(164,036,000)	(212,197,000)
Other	(2,122,000)	(782,000)	(1,105,000)
Cash Used for Investing Activities	(205,261,000)	(164,818,000)	(213,302,000)
Financing Activities:
Distributions to parent from noncontrolling interest	(21,500,000)	(23,500,000)	(22,000,000)
Capital contributions from parent	30,000,000	30,500,000	0
Repayment of long-term debt	(38,959,000)	(4,553,000)	(24,453,000)
Issuance of long-term debt	19,300,000	50,000,000	100,000,000
Proceeds from (Repayments of) short-term debt	52,500,000	(13,000,000)	9,000,000
Other	(1,523,000)	(1,640,000)	(662,000)
Cash Provided by (Used for) Financing Activities	39,818,000	37,807,000	61,885,000
Change in cash, cash equivalents, and restricted cash:	875,000	(1,141,000)	(3,423,000)
Cash, cash equivalents, and restricted cash at beginning of period	5,529,000	6,670,000	10,093,000
Cash, cash equivalents, and restricted cash at end of period	6,404,000	5,529,000	6,670,000
Supplemental disclosures of cash flow information:
Interest paid	23,898,000	23,171,000	20,018,000
Income taxes paid	0	95,000	0
Income taxes received	0	(249,000)	(59,000)
Significant noncash investing activities:
Accrued capital expenditures	$ 5,719,000	$ 26,697,000	$ 11,129,000