Consolidated Statements of Cash Flows (Unaudited) - USD ($)	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Operating Activities:
Net Income	$ 70,212,000	$ 67,858,000
Items not affecting cash:
Depreciation and amortization	53,423,000	41,754,000
Deferred income taxes	4,864,000	2,352,000
Provision for doubtful receivables	978,000	642,000
Employee benefit plan credit	(2,866,000)	(1,544,000)
Equity earnings in ATC	(6,879,000)	(6,113,000)
Other items	692,000	31,000
Changes in working capital items:
Decrease in current assets	14,307,000	25,530,000
Increase (decrease) in current liabilities	(24,088,000)	6,026,000
Dividends from ATC	5,526,000	5,336,000
Cash contributions to pension and other postretirement plans	(3,707,000)	(3,967,000)
Other noncurrent items, net	(760,000)	527,000
Cash Provided by Operating Activities	111,702,000	138,432,000
Investing Activities:
Capital expenditures	(128,389,000)	(149,001,000)
Capital contributions to investments	(5,894,000)	(4,801,000)
Other	(248,000)	368,000
Cash Used for Investing Activities	(134,531,000)	(153,434,000)
Financing Activities:
Cash dividends paid on common stock	(35,622,000)	(34,062,000)
Repayment of long-term debt	(3,405,000)	(23,330,000)
Issuance of long-term debt	0	100,000,000
Proceeds from (repayments of) short-term debt	41,500,000	(4,000,000)
Other	(1,331,000)	(659,000)
Cash Provided by Financing Activities	1,142,000	37,949,000
Change in cash, cash equivalents, and restricted cash	(21,687,000)	22,947,000
Cash, cash equivalents, and restricted cash at beginning of period	84,929,000	112,094,000
Cash, cash equivalents, and restricted cash at end of period	63,242,000	135,041,000
Significant noncash investing activities:
Accrued capital expenditures	16,819,000	10,991,000
MGE [Member]
Operating Activities:
Net Income	64,764,000	62,775,000
Items not affecting cash:
Depreciation and amortization	53,423,000	41,754,000
Deferred income taxes	3,653,000	(580,000)
Provision for doubtful receivables	978,000	642,000
Employee benefit plan credit	(2,866,000)	(1,544,000)
Other items	1,653,000	768,000
Changes in working capital items:
Decrease in current assets	14,236,000	24,864,000
Increase (decrease) in current liabilities	(22,234,000)	9,941,000
Cash contributions to pension and other postretirement plans	(3,707,000)	(3,967,000)
Other noncurrent items, net	(880,000)	374,000
Cash Provided by Operating Activities	109,020,000	135,027,000
Investing Activities:
Capital expenditures	(128,389,000)	(149,001,000)
Other	(477,000)	(680,000)
Cash Used for Investing Activities	(128,866,000)	(149,681,000)
Financing Activities:
Distributions to parent from noncontrolling interest	(17,000,000)	(19,000,000)
Repayment of long-term debt	(3,405,000)	(23,330,000)
Issuance of long-term debt	0	100,000,000
Proceeds from (repayments of) short-term debt	41,500,000	(4,000,000)
Other	(1,133,000)	(659,000)
Cash Provided by Financing Activities	19,962,000	53,011,000
Change in cash, cash equivalents, and restricted cash	116,000	38,357,000
Cash, cash equivalents, and restricted cash at beginning of period	6,670,000	10,093,000
Cash, cash equivalents, and restricted cash at end of period	6,786,000	48,450,000
Significant noncash investing activities:
Accrued capital expenditures	$ 16,819,000	$ 10,991,000