Employee Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2024

Retirement Benefits [Abstract]

Schedule of Amounts Recognized in Balance Sheet

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)

Schedule of Accumulated and Projected Benefit Obligations

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 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

Schedule of Net Benefit Costs

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

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

Defined Benefit Plan, Assumptions

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	%

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

Schedule of Health Care Cost Trend Rates

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

Schedule of Expected Benefit Payments

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

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

Schedule of Allocation of Plan Assets

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 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.

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).

Schedule of Multiemployer Plans

	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