Pension Plans and Other Postretirement Benefits (Tables)

12 Months Ended

Dec. 31, 2023

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:	2023			2022			2023			2022
Net benefit obligation as of January 1,	$	335,288		$	460,666		$	63,828		$	84,526
Service cost		2,892			5,064			780			1,293
Interest cost		17,319			11,161			3,308			1,940
Plan participants' contributions		—			—			1,017			986
Actuarial loss (gain)(a)		11,946			(120,166	)		1,951			(19,484	)
Plan amendments		—			—			(242	)		—
Gross benefits paid		(20,985	)		(21,437	)		(5,986	)		(5,725	)
Less: federal subsidy on benefits paid(b)		—			—			317			292
Benefit obligation as of December 31,	$	346,460		$	335,288		$	64,973		$	63,828
Change in Plan Assets:
Fair value of plan assets as of January 1,	$	370,171		$	473,953		$	41,867		$	54,844
Actual return on plan assets		53,346			(84,562	)		5,312			(8,958	)
Employer contributions		2,203			2,217			939			720
Plan participants' contributions		—			—			1,017			986
Gross benefits paid		(20,985	)		(21,437	)		(5,986	)		(5,725	)
Fair value of plan assets at end of year		404,735			370,171			43,149			41,867
Funded Status as of December 31,	$	58,275		$	34,883		$	(21,824	)	$	(21,961	)

(a)In 2022, higher discount rates were the primary driver of the actuarial gain.

(b)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, 2023 and 2022, 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)	2023			2022			2023			2022
Long-term asset	$	93,896		$	68,872		$	—		$	—
Current liability		(2,387	)		(2,408	)		—			—
Long-term liability		(33,234	)		(31,581	)		(21,824	)		(21,961	)
Net asset (liability)	$	58,275		$	34,883		$	(21,824	)	$	(21,961	)

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 assets in the consolidated balance sheets:

	Pension Benefits				Other Postretirement Benefits
(In thousands)	2023		2022		2023			2022
Net actuarial loss (gain)	$	33,237	$	51,148	$	(1,626	)	$	(1,085	)
Prior service benefit		—		—		(242	)		—
Transition obligation		—		—		5			9
Total	$	33,237	$	51,148	$	(1,863	)	$	(1,076	)

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	2023		2022
Projected benefit obligation, end of year	$	35,621	$	33,989
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	2023		2022		2023		2022
Accumulated benefit obligation, end of year	$	34,387	$	33,211	$	64,973	$	63,828
Fair value of plan assets, end of year		—		—		43,149		41,867

Net Periodic Benefit Costs

(In thousands)	Pension Benefits									Other Postretirement Benefits
Components of Net Periodic Benefit Cost:	2023			2022			2021			2023			2022			2021
Service cost	$	2,892		$	5,064		$	5,730		$	780		$	1,293		$	1,448
Interest cost		17,319			11,161			9,109			3,308			1,940			1,549
Expected return on assets		(25,248	)		(31,391	)		(29,487	)		(2,595	)		(3,365	)		(3,277	)
Amortization of:
Transition obligation		—			—			—			3			3			3
Prior service (credit) cost		—			(20	)		(124	)		—			(297	)		(1,518	)
Actuarial loss		1,760			2,416			6,646			(190	)		145			493
Net periodic benefit cost (credit)	$	(3,277	)	$	(12,770	)	$	(8,126	)	$	1,306		$	(281	)	$	(1,302	)

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
	2023			2022			2023			2022
Discount rate		5.10	%		5.47	%		5.11	%		5.45	%
Rate of compensation increase		4.30	%		3.21	%	N/A			N/A
Assumed health care cost trend rates:
Health care cost trend rate assumed for next year	N/A			N/A				6.75	%		7.00	%
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			2032			2032

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
	2023			2022			2021			2023			2022			2021
Discount rate		5.47	%		2.94	%		2.70	%		5.45	%		2.85	%		2.52	%
Expected rate of return on plan assets		7.00	%		6.75	%		7.00	%		6.59	%		6.40	%		6.61	%
Rate of compensation increase		3.28	%		3.24	%		3.23	%	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, 2023 and 2022, and the target allocation for 2024, by asset category, follows:

	Target			Percentage of Plan Assets at Year End
	Allocation			2023			2022
Equity securities(a)		63.0	%		64.0	%		65.0	%
Fixed income securities		30.0	%		30.0	%		26.0	%
Real estate		7.0	%		6.0	%		9.0	%
Total		100.0	%		100.0	%		100.0	%

(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)	2023		2022
Cash and Cash Equivalents	$	2,079	$	1,715
Equity Securities:
U.S. Large Cap		132,047		121,884
U.S. Mid Cap		32,840		28,392
U.S. Small Cap		40,830		35,372
International Blend		78,294		75,843
Fixed Income Securities:
Short-Term Fund		7,465		3,807
High Yield Bond		22,273		17,895
Long Duration Bond		100,431		85,767
Real Estate		28,840		38,418
Insurance Continuance Fund		1,585		1,613
Fixed Rate Fund		1,200		1,332
Total	$	447,884	$	412,038

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
2024	$	21,650	$	5,489	$	(368	)	$	5,121
2025		21,884		5,707		(402	)		5,305
2026		22,155		5,665		(449	)		5,216
2027		22,516		5,607		(489	)		5,118
2028		22,760		5,578		(519	)		5,059
2029 - 2033		116,273		26,608		(2,971	)		23,637