Employee Benefit Plans

12 Months Ended

Dec. 31, 2024

Retirement Benefits [Abstract]

Employee Benefit Plans

Employee Benefit Plans

Pension and other postretirement benefit plans

The Company has noncontributory qualified defined benefit pension plans and other postretirement benefit plans for certain eligible employees. The Company uses a measurement date of December 31 for all of its pension and postretirement benefit plans.

Prior to 2013, defined benefit pension plan benefits and accruals for all nonunion and certain union plans were frozen and on June 30, 2015, the remaining union plan was frozen. These employees were eligible to receive additional defined contribution plan benefits.

Effective January 1, 2010, eligibility to receive retiree medical benefits was modified at certain of the Company's businesses. Employees who had attained age 55 with 10 years of continuous service by December 31, 2010, were provided the option to choose between a pre-65 comprehensive medical plan coupled with a Medicare supplement or a specified company funded Retiree Reimbursement Account, regardless of when they retire. All other eligible employees must meet the new eligibility criteria of age 60 and 10 years of continuous service at the time they retire to be eligible for a specified company funded Retiree Reimbursement Account. Employees hired after December 31, 2009, will not be eligible for retiree medical benefits.

In 2012, the Company modified health care coverage for certain retirees. Effective January 1, 2013, post-65 coverage was replaced by a fixed-dollar subsidy for retirees and spouses to be used to purchase individual insurance through a healthcare exchange.

In connection with the previously discussed separation of Knife River on May 31, 2023, Knife River's pension plan, including the associated assets and liabilities, was transferred to Knife River and therefore is no longer reflected as part of the Company. Also in connection with the separation, a remeasurement of the Company's postretirement plan and the Company's unfunded, non-qualified defined benefit plan were performed and the applicable liabilities from the plans relating to transferring employees were transferred to Knife River.

Changes in benefit obligation and plan assets and amounts recognized in the Consolidated Balance Sheets at December 31 were as follows:

	Pension Benefits				Other Postretirement Benefits
	2024		2023		2024		2023
Change in benefit obligation:	(In thousands)
Benefit obligation at beginning of year	$	275,586	$	278,286	$	39,590	$	40,315
Service cost	—		—		505		534
Interest cost	12,799		13,521		1,837		1,956
Plan participants' contributions	—		—		412		479
Actuarial (gain) loss	(11,040)		5,395		(3,420)		(215)
Benefits paid	(21,995)		(21,616)		(3,249)		(3,479)
Benefit obligation at end of year	255,350		275,586		35,675		39,590
Change in net plan assets:
Fair value of plan assets at beginning of year	248,558		242,031		79,234		76,640
Actual return on plan assets	1,152		20,576		2,297		5,518
Employer contribution	2,911		7,567		71		76
Plan participants' contributions	—		—		412		479
Benefits paid	(21,995)		(21,616)		(3,249)		(3,479)
Fair value of net plan assets at end of year	230,626		248,558		78,765		79,234
Funded status - (under) over	$	(24,724)	$	(27,028)	$	43,090	$	39,644
Amounts recognized in the Consolidated Balance Sheets at December 31:
Noncurrent assets - other	$	—	$	—	$	43,090	$	39,644
Noncurrent liabilities - other	24,724		27,028		—		—
Benefit obligation (liabilities) assets - net amount recognized	$	(24,724)	$	(27,028)	$	43,090	$	39,644
Amounts recognized in accumulated other comprehensive loss:
Actuarial loss (gain)	$	13,228	$	32,273	$	(809)	$	(3,515)
Prior service credit	—		—		(37)		(115)
Total	$	13,228	$	32,273	$	(846)	$	(3,630)
Amounts recognized in regulatory assets or liabilities:
Actuarial loss (gain)	$	139,962	$	140,232	$	(1,478)	$	(1,146)
Prior service credit	—		—		(1,303)		(2,619)
Total	$	139,962	$	140,232	$	(2,781)	$	(3,765)

Employer contributions and benefits paid in the preceding table include only those amounts contributed directly to, or paid directly from, plan assets. Amounts related to regulated operations are recorded as regulatory assets or liabilities and are expected to be reflected in rates charged to customers over time. For more information on regulatory assets and liabilities, see Note 6.

In 2024, the actuarial gain recognized in the benefit obligation was primarily the result of an increase in the discount rate. In 2023, the actuarial loss recognized in the benefit obligation was primarily the result of a decrease in the discount rate. For more information on the discount rates, see the table below. Unrecognized pension actuarial gains and losses in excess of 10 percent of the greater of the projected benefit obligation or the market-related value of assets are amortized over the average life expectancy of plan participants for frozen plans. The market-related value of assets is determined using a five-year average of assets.

The pension plans all have accumulated benefit obligations in excess of plan assets. The projected benefit obligation, accumulated benefit obligation and fair value of plan assets for these plans at December 31 were as follows:

	2024		2023
	(In thousands)
Projected benefit obligation	$	255,350	$	275,586
Accumulated benefit obligation	$	255,350	$	275,586
Fair value of plan assets	$	230,626	$	248,558

The components of net periodic benefit cost (credit), other than the service cost component, are included in other income on the Consolidated Statements of Income. Prior service credit is amortized on a straight-line basis over the average remaining service period of active participants. These components related to the Company's pension and other postretirement benefit plans for the years ended December 31 were as follows:

	Pension Benefits						Other Postretirement Benefits
	2024		2023		2022		2024		2023		2022
Components of net periodic benefit cost (credit):	(In thousands)
Service cost	$	—	$	—	$	—	$	505	$	534	$	894
Interest cost	12,799		13,521		9,396		1,837		1,956		1,383
Expected return on assets	(16,113)		(17,194)		(17,482)		(5,315)		(5,361)		(5,277)
Amortization of prior service credit	—		—		—		(1,318)		(1,318)		(1,318)
Recognized net actuarial loss (gain)	4,149		3,093		5,826		(288)		(504)		(570)
Net periodic benefit cost (credit), including amount capitalized	835		(580)		(2,260)		(4,579)		(4,693)		(4,888)
Less amount capitalized	—		—		—		—		107		175
Net periodic benefit cost (credit)	835		(580)		(2,260)		(4,579)		(4,800)		(5,063)
Other changes in plan assets and benefit obligations recognized in accumulated comprehensive loss:
Net loss (gain)	401		187		2,369		71		(604)		(4,141)
Amortization of actuarial (loss) gain	(359)		(292)		(1,310)		130		108		(281)
Amortization of prior service credit	—		—		—		45		78		125
Reclassification of postretirement liability adjustment from regulatory asset	—		—		5,343		—		—		(992)
Total recognized in accumulated other comprehensive loss	42		(105)		6,402		246		(418)		(5,289)
Other changes in plan assets and benefit obligations recognized in regulatory assets or liabilities:
Net loss (gain)	3,520		1,826		9,757		(472)		(107)		11,920
Amortization of actuarial (loss) gain	(3,790)		(2,801)		(5,373)		158		304		500
Amortization of prior service credit	—		—		—		1,273		1,273		1,273
Reclassification of postretirement liability adjustment from regulatory asset	—		—		(5,343)		—		—		992
Total recognized in regulatory assets or liabilities	(270)		(975)		(959)		959		1,470		14,685
Total recognized in net periodic benefit credit, accumulated other comprehensive loss and regulatory assets or liabilities	$	607	$	(1,660)	$	3,183	$	(3,374)	$	(3,748)	$	4,333

Weighted average assumptions used to determine benefit obligations at December 31 were as follows:

	Pension Benefits				Other Postretirement Benefits
	2024		2023		2024		2023
Discount rate	5.41	%	4.84	%	5.43	%	4.85	%
Expected return on plan assets	6.50	%	6.50	%	6.00	%	6.00	%

Weighted average assumptions used to determine net periodic benefit cost (credit) for the years ended December 31 were as follows:

	Pension Benefits				Other Postretirement Benefits
	2024		2023		2024		2023
Discount rate	4.84	%	5.06	%	4.85	%	5.07	%
Expected return on plan assets	6.50	%	6.50	%	6.00	%	6.00	%

The expected rate of return on pension plan assets is based on a targeted asset allocation range determined by the funded ratio of the plan. As of December 31, 2024, the expected rate of return on pension plan assets is based on the targeted asset allocation range of 40 percent to 50 percent equity securities and 50 percent to 60 percent fixed-income securities and the expected rate of return from these asset categories. The expected rate of return on other postretirement plan assets is based on the targeted asset allocation range of 10 percent to 20 percent equity securities and 80 percent to 90 percent fixed-income securities and the expected rate of return from these asset categories. The expected return on plan assets for other postretirement benefits reflects insurance-related investment costs.

Health care rate assumptions for the Company's other postretirement benefit plans as of December 31 were as follows:

	2024		2023
Health care trend rate assumed for next year (pre-65/post-65)	8.5%/6.25%		7.5%/6.5%
Health care cost trend rate - ultimate	4.5	%	4.5	%
Year in which ultimate trend rate achieved (pre-65/post-65)	2035/2034		2034/2033

The Company's other postretirement benefit plans include health care and life insurance benefits for certain retirees. The plans underlying these benefits may require contributions by the retiree depending on such retiree's age and years of service at retirement or the date of retirement. The Company contributes a flat dollar amount to the monthly premiums which is updated annually on January 1.

The Company expects to contribute to its defined benefit pension plans in 2025 the minimum funding requirement of $1.7 million. The Company expects to contribute approximately $18,000 to its postretirement benefit plans in 2025.

The following benefit payments, which reflect future service, as appropriate, and expected Medicare Part D subsidies at December 31, 2024, are as follows:

Years	Pension Benefits		Other Postretirement Benefits		Expected Medicare Part D Subsidy
			(In thousands)
2025	$	22,280	$	3,333	$	48
2026	$	22,070	$	3,235	$	43
2027	$	21,870	$	3,153	$	37
2028	$	21,500	$	3,064	$	32
2029	$	21,170	$	2,941	$	27
2030-2034	$	98,020	$	13,659	$	85

Outside investment managers manage the Company's pension and postretirement assets. The Company's investment policy with respect to pension and other postretirement assets is to make investments solely in the interest of the participants and beneficiaries of the plans and for the exclusive purpose of providing benefits accrued and defraying the reasonable expenses of administration. The Company strives to maintain investment diversification to assist in minimizing the risk of large losses. The Company's policy guidelines allow for investment of funds in cash equivalents, fixed-income securities and equity securities. The guidelines prohibit investment in commodities and futures contracts, equity private placement, employer securities, leveraged or derivative securities, options, direct real estate investments, precious metals, venture capital and limited partnerships. The guidelines also prohibit short selling and margin transactions. The Company's practice is to periodically review and rebalance asset categories based on its targeted asset allocation percentage policy.

Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the measurement date. The fair value ASC establishes a hierarchy for grouping assets and liabilities, based on the significance of inputs. The estimated fair values of the Company's pension plans' assets are determined using the market approach.

The carrying value of the pension plans' Level 2 cash equivalents approximates fair value and is determined using observable inputs in active markets or the net asset value of shares held at year end, which is determined using other observable inputs including pricing from outside sources.

The estimated fair value of the pension plans' Level 1 and Level 2 equity securities are based on the closing price reported on the active market on which the individual securities are traded or other known sources including pricing from outside sources. The estimated fair value of the pension plans' Level 1 and Level 2 collective and mutual funds are based on the net asset value of shares held at year end, based on either published market quotations on active markets or other known sources including pricing from outside sources. The estimated fair value of the pension plans' Level 2 corporate and municipal bonds is determined using other observable inputs, including benchmark yields, reported trades, broker/dealer quotes, bids, offers, future cash flows and other reference data. The estimated fair value of the pension plans' Level 1 U.S. Government securities are valued based on quoted prices on an active market. The estimated fair value of the pension plans' Level 2 U.S. Government securities are valued mainly using other observable inputs, including benchmark yields, reported trades, broker/dealer quotes, bids, offers, to be announced prices, future cash flows and other reference data. The estimated fair value of the pension plans' Level 2 pooled separate accounts are determined using observable inputs in active markets or the net asset value of shares held at year end, or other observable inputs. Some of these securities are valued using pricing from outside sources.

All investments measured at net asset value in the tables that follow are invested in commingled funds, separate accounts or common collective trusts which do not have publicly quoted prices. The fair value of the commingled funds, separate accounts and common collective trusts are determined based on the net asset value of the underlying investments. The fair value of the underlying investments held by the commingled funds, separate accounts and common collective trusts is generally based on quoted prices in active markets.

Though the Company believes the methods used to estimate fair value are consistent with those used by other market participants, the use of other methods or assumptions could result in a different estimate of fair value.

The fair value of the Company's pension plans' assets (excluding cash) by class were as follows:

	Fair Value Measurements  at December 31, 2024, Using
	Quoted Prices in Active Markets for Identical Assets  (Level 1)		Significant Other Observable Inputs  (Level 2)		Significant Unobservable  Inputs  (Level 3)		Balance at December 31, 2024
	(In thousands)
Assets:
Cash equivalents	$	—	$	4,512	$	—	$	4,512
Equity securities:
U.S. companies	(2)		—		—		(2)
Collective and mutual funds (a)	72,777		93,606		—		166,383
U.S. Government securities	33,616		25,857		—		59,473
Investments measured at net asset value (b)	—		—		—		260
Total assets measured at fair value	$	106,391	$	123,975	$	—	$	230,626

(a)Collective and mutual funds invest approximately 39 percent in corporate bonds, 19 percent in U.S. Government securities, 17 percent in other investments, 15 percent in common stock of international companies, 9 percent in common stock of large-cap and mid-cap U.S. companies, and 1 percent cash and cash equivalents.

(b)In accordance with ASC 820 - Fair Value Measurements, certain investments that were measured at net asset value per share (or its equivalent) have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the line items presented in the Consolidated Balance Sheets.

	Fair Value Measurements  at December 31, 2023, Using
	Quoted Prices in Active Markets for Identical Assets  (Level 1)		Significant Other Observable Inputs  (Level 2)		Significant Unobservable  Inputs  (Level 3)		Balance at December 31, 2023
	(In thousands)
Assets:
Cash equivalents	$	—	$	7,197	$	—	$	7,197
Equity securities:
U.S. companies	(2)		—		—		(2)
Collective and mutual funds (a)	84,761		88,219		—		172,980
U.S. Government securities	30,162		33,141		—		63,303
Investments measured at net asset value (b)	—		—		—		5,080
Total assets measured at fair value	$	114,921	$	128,557	$	—	$	248,558

(a)Collective and mutual funds invest approximately 51 percent in corporate bonds, 15 percent in common stock of international companies, 11 percent in common stock of large-cap and mid-cap U.S. companies, 7 percent cash and cash equivalents, 7 percent in U.S. Government securities and 9 percent in other investments.

(b)In accordance with ASC 820 - Fair Value Measurements, certain investments that were measured at net asset value per share (or its equivalent) have not been classified in the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of the fair value hierarchy to the line items presented in the Consolidated Balance Sheets.

The estimated fair values of the Company's other postretirement benefit plans' assets are determined using the market approach.

The estimated fair value of the other postretirement benefit plans' Level 2 cash equivalents is valued at the net asset value of shares held at year end, based on published market quotations on active markets, or using other known sources including pricing from outside sources. The estimated fair value of the other postretirement benefit plans' Level 1 and Level 2 equity securities is based on the closing price reported on the active market on which the individual securities are traded or other known sources including pricing from outside sources. The estimated fair value of the other postretirement benefit plans' Level 2 insurance contract is based on contractual cash surrender values that are determined primarily by investments in managed separate accounts of the insurer. These amounts approximate fair value. The managed separate accounts are valued based on other observable inputs or corroborated market data.

Though the Company believes the methods used to estimate fair value are consistent with those used by other market participants, the use of other methods or assumptions could result in a different estimate of fair value.

The fair value of the Company's other postretirement benefit plans' assets (excluding cash) by asset class were as follows:

	Fair Value Measurements  at December 31, 2024, Using
	Quoted Prices in Active Markets for Identical Assets  (Level 1)		Significant Other Observable Inputs  (Level 2)		Significant Unobservable  Inputs  (Level 3)		Balance at December 31, 2024
	(In thousands)
Assets:
Cash equivalents	$	—	$	4,373	$	—	$	4,373
Equity securities:
U.S. companies	2,880		—		—		2,880
Insurance contract (a)	—		71,512		—		71,512
Total assets measured at fair value	$	2,880	$	75,885	$	—	$	78,765

(a)The insurance contract invests approximately 41 percent in corporate bonds, 28 percent in U.S. Government securities, 19 percent in common stock of large-cap U.S. companies, 6 percent in common stock of small-cap U.S. companies and 6 percent in other investments.

	Fair Value Measurements  at December 31, 2023, Using
	Quoted Prices in Active Markets for Identical Assets  (Level 1)		Significant Other Observable Inputs  (Level 2)		Significant Unobservable  Inputs  (Level 3)		Balance at December 31, 2023
	(In thousands)
Assets:
Cash equivalents	$	—	$	4,562	$	—	$	4,562
Equity securities:
U.S. companies	2,369		—		—		2,369
Insurance contract (a)	—		72,303		—		72,303
Total assets measured at fair value	$	2,369	$	76,865	$	—	$	79,234

(a)The insurance contract invests approximately 60 percent in corporate bonds, 16 percent in common stock of large-cap U.S. companies, 15 percent in U.S. Government securities, 5 percent in common stock of small-cap U.S. companies and 4 percent in other investments.

Nonqualified benefit plans

In addition to the qualified defined benefit pension plans reflected in the table at the beginning of this note, the Company also has unfunded, nonqualified defined benefit plans for executive officers and certain key management employees that generally provide for defined benefit payments at age 65 following the employee's retirement or, upon death, to their beneficiaries for a 15-year period. In February 2016, the Company froze the unfunded, nonqualified defined benefit plans to new participants and eliminated benefit increases. Vesting for participants not fully vested was retained.

The projected benefit obligation and accumulated benefit obligation for these plans at December 31 were as follows:

	2024		2023
	(In thousands)
Projected benefit obligation	$	52,007	$	57,033
Accumulated benefit obligation	$	52,007	$	57,033

The components of net periodic benefit cost are included in other income on the Consolidated Statements of Income. These components related to the Company's nonqualified defined benefit plans for the years ended December 31 were as follows:

	2024		2023		2022
	(In thousands)
Components of net periodic benefit cost:
Interest cost	$	2,568	$	2,740	$	1,681
Recognized net actuarial loss	365		273		911
Net periodic benefit cost	$	2,933	$	3,013	$	2,592

Weighted average assumptions used at December 31 were as follows:

	2024		2023
Benefit obligation discount rate	5.26	%	4.73	%
Benefit obligation rate of compensation increase	N/A		N/A
Net periodic benefit cost discount rate	4.73	%	4.97	%
Net periodic benefit cost rate of compensation increase	N/A		N/A

The amount of future benefit payments for the unfunded, nonqualified defined benefit plans at December 31, 2024, are expected to aggregate as follows:

	2025		2026		2027		2028		2029		2030-2034
	(In thousands)
Nonqualified benefits	$	5,700	$	5,610	$	5,830	$	5,560	$	5,190	$	20,920

In 2012, the Company established a nonqualified defined contribution plan for certain key management employees. In 2020, the plan was frozen to new participants and no new Company contributions will be made to the plan after December 31, 2020. Vesting for participants not fully vested was retained. A new nonqualified defined contribution plan was adopted in 2020, effective January 1, 2021, to replace the plan originally established in 2012 with similar provisions. Expenses incurred under these plans for 2024, 2023 and 2022 were $4.0 million, $2.7 million and $538,000, respectively.

The amount of investments that the Company anticipates using to satisfy obligations under these plans at December 31 was as follows:

	2024		2023
	(In thousands)
Investments
Insurance contracts*	$	59,282	$	62,936
Life insurance**	30,834		31,303
Other	12,879		6,409
Total investments	$	102,995	$	100,648

*For more information on the insurance contracts, see Note 9.

**Investments of life insurance are carried on plan participants (payable upon the employee's death).

Defined contribution plans

The Company sponsors a defined contribution plan for eligible employees and the costs incurred under this plan were $10.7 million in 2024, $17.0 million in 2023 and $14.3 million in 2022.

Multiemployer plans

The Company contributes to a MEPP under the terms of a collective-bargaining agreement that covers its union-represented employees. The risks of participating in this multiemployer plan is different from single-employer plans in the following aspects:

•Assets contributed to the MEPP by one employer may be used to provide benefits to employees of other participating employers

•If a participating employer stops contributing to the plan, the unfunded obligations of the plan may be borne by the remaining participating employers

•If the Company chooses to stop participating in its MEPP, the Company may be required to pay those plans an amount based on the underfunded status of the plan, referred to as a withdrawal liability

The Company's participation in this plan is outlined in the following table. Unless otherwise noted, the most recent Pension Protection Act zone status available in 2024 and 2023 is for the plan's year-end status at December 31, 2023, and December 31, 2022, respectively. The zone status is based on information that the Company received from the plan and is certified by the plan's actuary. Among other factors, a plan in the red zone is generally less than 65 percent funded, a plan in the yellow zone is between 65 percent and 80 percent funded, and a plan in the green zone is at least 80 percent funded.

	EIN/Pension Plan Number	Pension Protection Act Zone Status		FIP/RP Status Pending/Implemented	Contributions						Surcharge Imposed	Expiration Date of Collective Bargaining Agreement
Pension Fund		2024	2023		2024		2023		2022
					(In thousands)
Idaho Plumbers and Pipefitters Pension Plan	826010346-001	Green as of 5/31/2024	Green as of 5/31/2023	No	$	1,434	$	1,690	$	1,613	No	3/31/2027
Total contributions					$	1,434	$	1,690	$	1,613

The Company was listed in the plans' Forms 5500 as providing more than 5 percent of the total contributions for the following plans and plan years:

Pension Fund	Year Contributions to Plan Exceeded More Than 5 Percent of Total Contributions (as of December 31 of the Plan's Year-End)
Idaho Plumbers and Pipefitters Pension Plan	2023 and 2022