EMPLOYEE BENEFIT PLANS (Tables)

12 Months Ended

Sep. 30, 2023

Retirement Benefits [Abstract]

Summary of Changes in Funded Status of Plans and Liabilities Recognized

The following summarizes the changes in the funded status of the plans and the related liabilities recognized on the Consolidated Balance Sheets as of September 30:

	Pension (1)				OPEB
(Thousands)	2023		2022		2023		2022
Change in Benefit Obligation
Benefit obligation at beginning of year	$	290,823	$	395,547	$	173,217	$	244,674
Service cost	5,402		8,291		2,471		4,305
Interest cost	15,174		9,632		9,146		6,355
Plan participants’ contributions (2)	32		59		552		423
Actuarial (gain) loss	(7,057)		(109,320)		25,363		(77,775)
Benefits paid, net of retiree subsidies received	(14,053)		(13,386)		(7,343)		(4,765)
Benefit obligation at end of year	$	290,321	$	290,823	$	203,406	$	173,217
Change in plan assets
Fair value of plan assets at beginning of year	$	284,347	$	355,284	$	99,736	$	114,183
Actual return (loss) on plan assets	27,456		(58,239)		9,826		(15,996)
Employer contributions	579		628		4,192		6,082
Benefits paid, net of plan participants’ contributions (2)	(14,021)		(13,326)		(6,971)		(4,533)
Fair value of plan assets at end of year	$	298,361	$	284,347	$	106,783	$	99,736
Funded status	$	8,040	$	(6,476)	$	(96,623)	$	(73,481)
Amounts recognized on Consolidated Balance Sheets
Postemployment employee benefit asset
Noncurrent	$	18,684	$	4,388	$	—	$	—
Postemployment employee benefit liability
Current	$	(538)	$	(578)	$	(4,201)	$	(900)
Noncurrent	(10,106)		(10,286)		(92,422)		(72,581)
Total	$	8,040	$	(6,476)	$	(96,623)	$	(73,481)

(1)Includes the Company’s PEP.

(2)Employees hired prior to July 1, 1998, that were eligible to elect an additional participant contribution to enhance their benefits, and contributions made during the periods were immaterial.

Summary of Regulatory Assets and Accumulated Other Comprehensive Income

The following table summarizes the amounts recognized in regulatory assets and accumulated OCI as of September 30:

	Regulatory Assets				Accumulated Other Comprehensive Income (Loss)
(Thousands)	Pension		OPEB		Pension		OPEB
Balance at September 30, 2021	$	56,187	$	60,335	$	22,790	$	12,696
Amounts arising during the period:
Net actuarial (gain)	(14,922)		(35,781)		(14,885)		(18,422)
Amounts amortized to net periodic costs:
Net actuarial (loss)	(5,843)		(4,577)		(2,902)		(1,107)
Prior service (cost) credit	(101)		133		—		11
Balance at September 30, 2022	$	35,321	$	20,110	$	5,003	$	(6,822)
Amounts arising during the period:
Net actuarial (gain) loss	(10,493)		9,936		(4,048)		12,320
Amounts amortized to net periodic costs:
Net actuarial (loss)	(87)		—		(213)		—
Prior service (cost)	(103)		—		—		—
Balance at September 30, 2023	$	24,638	$	30,046	$	742	$	5,498

The amounts in regulatory assets and accumulated OCI not yet recognized as components of net periodic benefit cost as of September 30 are:

	Regulatory Assets								Accumulated Other Comprehensive Income (Loss)
	Pension				OPEB				Pension				OPEB
(Thousands)	2023		2022		2023		2022		2023		2022		2023		2022
Net actuarial loss (gain)	$	24,577	$	35,157	$	30,046	$	20,110	$	742	$	5,003	$	5,498	$	(6,822)
Prior service cost	61		164		—		—		—		—		—		—
Total	$	24,638	$	35,321	$	30,046	$	20,110	$	742	$	5,003	$	5,498	$	(6,822)

Amounts included in regulatory assets and accumulated OCI expected to be recognized as components of net periodic benefit cost in fiscal 2024 are as follows:

	Regulatory Assets				Accumulated Other Comprehensive Income (Loss)
(Thousands)	Pension		OPEB		Pension		OPEB
Net actuarial loss (gain)	$	815	$	667	$	(12)	$	661
Prior service cost	62		—		—		—
Total	$	877	$	667	$	(12)	$	661

Schedule of Accumulated Benefit Obligations in Excess of Fair Value of Plan Assets

The projected benefit and accumulated benefit obligations and the fair value of plan assets as of September 30, are as follows:

	Pension
(Thousands)	2023		2022
Projected benefit obligation	$	290,321	$	290,823
Accumulated benefit obligation	$	267,794	$	265,933
Fair value of plan assets	$	298,361	$	284,347

Components of Net Periodic Cost

The components of the net periodic cost for pension benefits, including the Company’s PEP, and OPEB costs (principally health care and life insurance) for employees and covered dependents for fiscal years ended September 30, are as follows:

	Pension						OPEB
(Thousands)	2023		2022		2021		2023		2022		2021
Service cost	$	5,402	$	8,291	$	8,730	$	2,471	$	4,305	$	4,844
Interest cost	15,174		9,632		9,112		9,146		6,355		6,071
Expected return on plan assets	(19,972)		(21,275)		(20,150)		(6,721)		(7,575)		(6,497)
Recognized actuarial loss	300		8,745		11,446		—		5,684		7,909
Prior service cost (credit) amortization	103		101		102		—		(144)		(179)
Net periodic benefit cost recognized as expense	$	1,007	$	5,494	$	9,240	$	4,896	$	8,625	$	12,148

Schedule of Weighted Average Assumptions Used

The weighted average assumptions used to determine the Company’s benefit costs during the fiscal years below and obligations as of September 30, are as follows:

	Pension									OPEB
	2023			2022			2021			2023			2022			2021
Benefit costs:
Discount rate	5.50/5.50%		(1)	3.10/3.07%		(1)	2.95/2.92%		(1)	5.51/5.51%		(1)	3.24/3.17%		(1)	3.08/3.03%		(1)
Expected asset return	7.00	%		6.75	%		6.75	%		7.00	%		6.75	%		6.75	%
Compensation increase	3.00/3.50%		(1)	3.00/3.50%		(1)	3.00/3.50%		(1)	3.00/3.50%		(1)	3.00/3.50%		(1)	3.00/3.50%		(1)
Obligations:
Discount rate	5.89/5.87%		(1)	5.50/5.50%		(1)	3.10/3.07%		(1)	5.97/5.94%		(1)	5.51/5.51%		(1)	3.24/3.17%		(1)
Compensation increase	3.00/3.50%		(1)	3.00/3.50%		(1)	3.00/3.50%		(1)	3.00/3.50%		(1)	3.00/3.50%		(1)	3.00/3.50%		(1)

(1)Percentages for represented and non-represented plans, respectively.

Summary of Pension and OPEB Assets

Information relating to the assumed HCCTR used to determine expected OPEB benefits as of September 30, and the effect of a 1% change in the rate, are as follows:

($ in thousands)	2023		2022		2021
HCCTR	7.4%		6.6%		6.9%
Ultimate HCCTR	4.5%		4.5%		4.5%
Year ultimate HCCTR reached	2032		2027		2027
Effect of a 1 percentage point increase in the HCCTR on:
Year-end benefit obligation	$	30,818	$	26,710	$	43,217
Total service and interest cost	$	2,117	$	2,544	$	2,959
Effect of a 1 percentage point decrease in the HCCTR on:
Year-end benefit obligation	$	(25,283)	$	(21,853)	$	(34,669)
Total service and interest costs	$	(1,700)	$	(1,966)	$	(2,253)

Pension and OPEB assets held in the master trust, measured at fair value, are summarized as follows:

	Pension				OPEB
(Thousands)	Quoted Prices in Active Markets for Identical Assets (Level 1)		Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Total
As of September 30, 2023
Assets
Registered Investment Companies:
Equity Funds:
Large Cap Index	81,171		81,171		30,884		30,884
Extended Market Index	17,256		17,256		6,444		6,444
International Stock	48,557		48,557		17,966		17,966
Fixed Income Funds:
Emerging Markets	11,471		11,471		4,306		4,306
Core Fixed Income	—		—		22,241		22,241
High Yield Bond Fund	20,685		20,685		7,651		7,651
Long Duration Fund	58,484		58,484		—		—
Total assets in the fair value hierarchy	$	237,624	237,624		$	89,492	89,492
Investments measured at net asset value
Collective investment trusts			60,737				17,291
Total assets at fair value			$	298,361			$	106,783
As of September 30, 2022
Assets
Money market funds	$	—	$	—	$	28	$	28
Registered Investment Companies:
Equity Funds:
Large Cap Index	75,394		75,394		26,939		26,939
Extended Market Index	15,783		15,783		5,578		5,578
International Stock	44,846		44,846		16,106		16,106
Fixed Income Funds:
Emerging Markets	11,074		11,074		4,026		4,026
Core Fixed Income	—		—		16,594		16,594
Opportunistic Income	—		—		3,283		3,283
Ultra Short Duration	—		—		3,296		3,296
High Yield Bond Fund	19,816		19,816		7,320		7,320
Long Duration Fund	59,084		59,084		—		—
Total assets in the fair value hierarchy	$	225,997	225,997		$	83,170	83,170
Investments measured at net asset value
Collective investment trusts			58,350				16,566
Total assets at fair value			$	284,347			$	99,736

Schedule of Mix and Targeted Allocation of Plan Assets

The mix and targeted allocation of the pension and OPEB plans’ assets are as follows:

	2024		Assets at
	Target		September 30,
Asset Allocation	Allocation		2023		2022
U.S. equity securities	34	%	34	%	32	%
International equity securities	17		16		16
Fixed income	33		31		32
Collective investment trusts at NAV	16		19		20
Total	100	%	100	%	100	%

Schedule of Expected Benefit Payments

The following benefit payments, which reflect expected future service, as appropriate, are expected to be paid during the following fiscal years:

(Thousands)	2024		2025		2026		2027		2028		2029 - 2033
Pension	$	15,227	$	16,233	$	17,255	$	18,246	$	19,219	$	110,341
OPEB	$	6,925	$	7,602	$	8,481	$	9,337	$	10,211	$	63,780

Schedule of Valuation Methodologies Used for Assets Measured at Fair Value

The following is a description of the valuation methodologies used for assets measured at fair value:

Asset Types	Description of the Valuation Methodologies
Money Market funds	Represents bank balances and money market funds that are valued based on the NAV of shares held at year end.
Registered Investment Companies	Equity and fixed income funds valued at the NAV of shares held by the plan at year end as reported on the active market on which the individual securities are traded.
Collective investment trusts	The NAV for collective investment trusts is provided by the Trustee and is used as a practical expedient to estimate fair value. The NAV is based on the value of the underlying assets owned by the fund less liabilities.