Pension Plans and Other Postretirement Benefits (Tables)

12 Months Ended

Dec. 31, 2025

Retirement Benefits [Abstract]

Schedule of Benefit Obligations and Change in Plan Assets

a.Benefit Obligations and Plan Assets.

(In thousands)	Pension Benefits						Other Postretirement Benefits
Change in Benefit Obligations:	2025			2024			2025			2024
Net benefit obligation as of January 1,	$	326,937		$	346,460		$	59,184		$	64,973
Service cost		2,612			3,078			743			856
Interest cost		17,139			17,118			3,028			3,126
Plan participants' contributions		—			—			1,081			1,045
Actuarial loss (gain)(a)		11,028			(16,669	)		289			(3,769	)
Settlements(b)		—			—			—			(1,227	)
Gross benefits paid		(22,239	)		(23,050	)		(6,299	)		(6,171	)
Less: federal subsidy on benefits paid(c)		—			—			354			351
Benefit obligation as of December 31,	$	335,477		$	326,937		$	58,380		$	59,184
Change in Plan Assets:
Fair value of plan assets as of January 1,	$	424,468		$	404,735		$	41,321		$	43,149
Actual return on plan assets		57,886			40,608			5,999			4,131
Employer contributions		2,304			2,175			739			682
Plan participants' contributions		—			—			1,081			1,045
Settlements(b)		—			—			—			(1,515	)
Gross benefits paid		(22,239	)		(23,050	)		(6,299	)		(6,171	)
Fair value of plan assets at end of year		462,419			424,468			42,841			41,321
Funded Status as of December 31,	$	126,942		$	97,531		$	(15,539	)	$	(17,863	)

(a)Changes in discount rates were the primary driver of the actuarial loss (gain) in 2025 and 2024.

(b)In August 2024, MGE entered into an agreement to transfer the mortality and investment risk, as well as the administration of, its employer-paid life insurance plan to a third party. MGE accounted for the settlement under the scope of ASC 715.

(c)In 2003, the Medicare Prescription Drug, Improvement and Modernization Act of 2003 was signed into law authorizing Medicare to provide prescription drug benefits to retirees. For both the years ended December 31, 2025 and 2024, the subsidy due to MGE was $0.3 million.

Schedule of Amounts Recognized in the Consolidated Balance Sheet

The amounts recognized in the consolidated balance sheets to reflect the funded status of the plans as of December 31 are as follows:

	Pension Benefits						Other Postretirement Benefits
(In thousands)	2025			2024			2025			2024
Long-term asset	$	162,493		$	131,418		$	2,492		$	846
Current liability		(2,477	)		(2,441	)		—			—
Long-term liability		(33,074	)		(31,446	)		(18,031	)		(18,709	)
Net asset (liability)	$	126,942		$	97,531		$	(15,539	)	$	(17,863	)

Amounts Recognized in Regulatory Asset

The following table shows the amounts that have not yet been recognized in our net periodic benefit cost as of December 31 and are recorded as regulatory asset (liability) in the consolidated balance sheets:

	Pension Benefits					Other Postretirement Benefits
(In thousands)	2025			2024		2025			2024
Net actuarial loss (gain)	$	(14,444	)	$	3,699	$	(9,575	)	$	(7,191	)
Transition obligation		—			—		—			3
Total	$	(14,444	)	$	3,699	$	(9,575	)	$	(7,188	)

Schedule of Projected Benefit Obligations in Excess of Plan Assets

The projected benefit obligation and fair value of plan assets for pension plans with a projected benefit obligation in excess of plan assets as of December 31 are as follows:

(In thousands)	Pension Benefits
Projected Benefit Obligation in Excess of Plan Assets	2025		2024
Projected benefit obligation, end of year	$	35,551	$	33,887
Fair value of plan assets, end of year		—		—

Schedule of Accumulated Benefit Obligations in Excess of Plan Assets

The accumulated benefit obligation and fair value of plan assets with an accumulated benefit obligation in excess of plan assets as of December 31 are as follows:

(In thousands)	Pension Benefits				Other Postretirement Benefits
Accumulated Benefit Obligation in Excess of Plan Assets	2025		2024		2025		2024
Accumulated benefit obligation, end of year	$	33,553	$	32,463	$	44,007	$	43,882
Fair value of plan assets, end of year		—		—		25,976		25,172

Net Periodic Benefit Costs

(In thousands)	Pension Benefits									Other Postretirement Benefits
Components of Net Periodic Benefit Cost:	2025			2024			2023			2025			2024			2023
Service cost	$	2,612		$	3,078		$	2,892		$	743		$	856		$	780
Interest cost		17,139			17,118			17,319			3,028			3,126			3,308
Expected return on assets		(29,014	)		(28,597	)		(25,248	)		(2,715	)		(2,725	)		(2,595	)
Settlement cost		—			—			—			—			288			—
Amortization of:
Transition obligation		—			—			—			3			3			3
Prior service credit		—			—			—			—			(242	)		—
Actuarial loss (gain)		299			859			1,760			(642	)		380			(190	)
Net periodic benefit cost (credit)	$	(8,964	)	$	(7,542	)	$	(3,277	)	$	417		$	1,686		$	1,306

Plan Assumptions

The weighted-average assumptions used to determine the benefit obligations were as follows for the years ended December 31:

	Pension Benefits						Other Postretirement Benefits
	2025			2024			2025			2024
Discount rate		5.45	%		5.64	%		5.34	%		5.59	%
Rate of compensation increase		3.58	%		3.81	%	N/A			N/A
Assumed health care cost trend rates:
Health care cost trend rate assumed for next year	N/A			N/A				7.25	%		7.50	%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate)	N/A			N/A				4.75	%		4.75	%
Year that the rate reaches the ultimate trend rate	N/A			N/A			2036			2036

The weighted-average assumptions used to determine the net periodic cost were as follows for the years ended December 31:

	Pension Benefits									Other Postretirement Benefits
	2025			2024			2023			2025			2024			2023
Discount rate		5.64	%		5.10	%		5.47	%		5.59	%		5.11	%		5.45	%
Expected rate of return on plan assets		7.00	%		7.24	%		7.00	%		7.00	%		6.81	%		6.59	%
Rate of compensation increase		3.83	%		4.32	%		3.28	%	N/A			N/A			N/A

Fair Value of Plan Assets by Asset Category

The asset allocation for MGE's pension plans as of December 31, 2025 and 2024, and the target allocation for 2026, by asset category, follows:

	Target			Percentage of Plan Assets at Year End
	Allocation(b)			2025			2024
Equity securities(a)		45	%		48	%		56	%
Fixed income securities		50	%		47	%		38	%
Real estate		5	%		5	%		6	%

(a)Target allocations for equity securities are broken out as follows: 32% United States equity and 13% non-United States equity.

(b)The target allocation for MGE's pension plans were approved to be rebalanced in December 2025. The trades happened in two steps, the first in December 2025 and the second in January 2026.

Other Postretirement Plan Assets

Other Postretirement plan assets are comprised of specific assets within certain defined benefit pension plans (401(h) assets) as well as assets held in VEBA trusts. The asset allocation for MGE's 401(h) assets as of December 31, 2025 and 2024, and the target allocation for 2026, by asset category, follows:

	Target			Percentage of Plan Assets at Year End
	Allocation			2025			2024
Equity securities(a)		63	%		65	%		66	%
Fixed income securities		30	%		29	%		28	%
Real estate		7	%		6	%		6	%

(a)Target allocations for equity securities are broken out as follows: 45.5% United States equity and 17.5% non-United States equity.

The fair values of MGE's plan assets by asset category as of December 31 are as follows:

(In thousands)	2025		2024
Cash and Cash Equivalents	$	695	$	772
Equity Securities:
U.S. Large Cap		118,871		128,262
U.S. Mid Cap		23,180		27,960
U.S. Small Cap		32,676		37,222
International Blend		72,948		73,444
Fixed Income Securities:
Short-Term Fund		18,467		7,231
High Yield Bond		25,154		24,231
Long Duration Bond		185,688		139,631
Real Estate		27,012		26,146
Fixed Rate Fund		569		890
Total	$	505,260	$	465,789

Benefit Payments, Fiscal Year Maturity

The following benefit payments, which reflect expected future service, as appropriate, are expected to be paid as follows:

	Pension		Other Postretirement Benefits
(In thousands)	Pension Benefits		Gross Postretirement Benefits		Expected Medicare Part D Subsidy			Net Postretirement Benefits
2026	$	22,689	$	5,404	$	(461	)	$	4,943
2027		22,878		5,415		(504	)		4,911
2028		23,123		5,383		(541	)		4,842
2029		23,297		5,311		(577	)		4,734
2030		23,392		5,247		(608	)		4,639
2031 - 2035		118,606		24,843		(3,410	)		21,433