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EMPLOYEE BENEFIT PLANS (Tables)
 12 Months Ended
Sep. 30, 2025
Retirement Benefits [Abstract]  
Schedule 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)2025202420252024
Change in Benefit Obligation
Benefit obligation at beginning of year$333,532 $290,321 $181,800 $203,406 
Service cost5,523 4,976 1,092 1,406 
Interest cost15,433 16,240 8,387 8,327 
Plan amendments— — — (79,881)
Plan participants’ contributions (2)
20 27 1,401 703 
Actuarial (gain) loss(12,216)36,863 39,942 54,518 
Benefits paid, net of retiree subsidies received(16,838)(14,895)(7,808)(6,679)
Benefit obligation at end of year$325,454 $333,532 $224,814 $181,800 
Change in plan assets
Fair value of plan assets at beginning of year$342,710 $298,361 $129,721 $106,783 
Actual return on plan assets28,156 58,682 12,063 21,249 
Employer contributions539 535 486 7,846 
Reimbursement from Trust (3)
— — (9,139)— 
Benefits paid, net of plan participants’ contributions (2)
(16,819)(14,868)(6,538)(6,157)
Fair value of plan assets at end of year$354,586 $342,710 $126,593 $129,721 
Funded status$29,132 $9,178 $(98,221)$(52,079)
Amounts recognized on Consolidated Balance Sheets
Postemployment employee benefit asset
Noncurrent$40,813 $21,104 $— $3,556 
Postemployment employee benefit liability
Current$(555)$(552)$(517)$(2,400)
Noncurrent(11,126)(11,374)(97,704)(53,235)
Total$29,132 $9,178 $(98,221)$(52,079)
(1)Includes the Company’s PEP.
(2)Contributions made by employees hired prior to July 1, 1998, who were eligible to elect an additional participant contribution to enhance their benefits, were immaterial during the periods.
(3)Reimbursements for benefit premiums paid by the Company on behalf of the Trust.
Schedule 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 AssetsAccumulated Other Comprehensive Income (Loss)
(Thousands)PensionOPEBPensionOPEB
Balance at September 30, 2023$24,638 $30,046 $742 $5,498 
Amounts arising during the period:
Net actuarial (gain) loss(2,407)27,108 934 14,080 
Prior service (credit)— (60,504)— (19,376)
Amounts amortized to net periodic costs:
Net actuarial gain (loss)2 (3,098)(119)(1,164)
Prior service (cost) credit(61)7,458 — 2,555 
Balance at September 30, 2024$22,172 $1,010 $1,557 $1,593 
Amounts arising during the period:
Net actuarial (gain) loss(13,368)27,178 (3,303)10,086 
Amounts amortized to net periodic costs:
Net actuarial (loss)(994)(5,114)(209)(2,057)
Prior service credit— 9,801 — 3,279 
Balance at September 30, 2025$7,810 $32,875 $(1,955)$12,901 

The amounts in regulatory assets and accumulated OCI not yet recognized as components of net periodic benefit cost as of September 30 are:
Regulatory AssetsAccumulated Other Comprehensive
Income (Loss)
PensionOPEBPensionOPEB
(Thousands)20252024202520242025202420252024
Net actuarial loss (gain)$7,810 $22,172 $76,120 $54,056 $(1,955)$1,557 $26,443 $18,414 
Prior service cost (credit)— — (43,245)(53,046)— — (13,542)(16,821)
Total$7,810 $22,172 $32,875 $1,010 $(1,955)$1,557 $12,901 $1,593 
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)20252024
Projected benefit obligation$325,454 $333,532 
Accumulated benefit obligation$302,880 $306,850 
Fair value of plan assets$354,586 $342,710 
Schedule of 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:
PensionOPEB
(Thousands)202520242023202520242023
Service cost$5,523 $4,976 $5,402 $1,092 $1,406 $2,471 
Interest cost15,433 16,240 15,174 8,387 8,327 9,146 
Expected return on plan assets(23,700)(20,346)(19,972)(9,385)(7,920)(6,721)
Recognized actuarial loss1,203 117 300 7,171 4,262 — 
Prior service cost (credit) amortization— 61 103 (13,080)(10,013)— 
Net periodic benefit cost recognized as expense$(1,541)$1,048 $1,007 $(5,815)$(3,938)$4,896 
Schedule of Weighted Average Assumptions Used
The weighted average assumptions used to determine the Company’s benefit costs during the fiscal years below and obligations as of September 30, are as follows:
PensionOPEB
202520242023202520242023
Benefit costs:
Discount rate
5.01/4.99%
(1)
5.89/5.87%
(1)
5.50/5.50%
(1)
4.97/4.98%
(1)
5.97/5.94%
(1)
5.51/5.51%
(1)
Expected asset return7.50 %7.00 %7.00 %7.50 %7.00 %7.00 %
Compensation increase
3.00/3.50%
(1)
3.00/3.50%
(1)
3.00/3.50%
(1)
3.00/3.50%
(1)
3.00/3.50%
(1)
3.00/3.50%
(1)
Obligations:
Discount rate
5.46/5.43%
(1)
5.01/4.99%
(1)
5.89/5.87%
(1)
5.35/5.35%
(1)
4.97/4.98%
(1)
5.97/5.94%
(1)
Compensation increase
3.00/3.50%
(1)
3.00/3.50%
(1)
3.00/3.50%
(1)
3.00/3.50%
(1)
3.00/3.50%
(1)
3.00/3.50%
(1)
(1)Percentages for represented and non-represented plans, respectively.
Schedule of Pension and OPEB Assets
Information relating to the assumed HCCTR used to determine expected OPEB benefits as of September 30, is as follows:
($ in thousands)202520242023
HCCTR9.4%8.8%7.4%
Ultimate HCCTR4.5%4.5%4.5%
Year ultimate HCCTR reached203320322032
Pension and OPEB assets held in the master trust, measured at fair value, are summarized as follows:
PensionOPEB
(Thousands)Quoted Prices in Active Markets for Identical Assets
(Level 1)		TotalQuoted Prices in Active Markets for Identical Assets
(Level 1)		Total
As of September 30, 2025
Assets
Registered Investment Companies:
Equity Funds:
Large Cap Index81,213 81,213 36,682 36,682 
Extended Market Index17,654 17,654 7,776 7,776 
International Stock52,876 52,876 22,243 22,243 
Fixed Income Funds:
Emerging Markets13,781 13,781 5,164 5,164 
Core Fixed Income— — 27,257 27,257 
High Yield Bond Fund16,864 16,864 8,798 8,798 
Long Duration Fund107,011 107,011 — — 
Total assets in the fair value hierarchy$289,399 289,399 $107,920 107,920 
Investments measured at net asset value
Collective investment trusts65,187 18,673 
Total assets at fair value$354,586 $126,593 
As of September 30, 2024
Assets
Money market funds$— $— $24 $24 
Registered Investment Companies:
Equity Funds:
Large Cap Index76,897 76,897 38,040 38,040 
Extended Market Index16,665 16,665 7,977 7,977 
International Stock50,549 50,549 22,730 22,730 
Fixed Income Funds:
Emerging Markets13,354 13,354 5,358 5,358 
Core Fixed Income— — 28,765 28,765 
High Yield Bond Fund16,704 16,704 9,195 9,195 
Long Duration Fund106,656 106,656 — — 
Total assets in the fair value hierarchy$280,825 280,825 $112,089 112,089 
Investments measured at net asset value
Collective investment trusts61,885 17,632 
Total assets at fair value$342,710 $129,721 
Schedule of Mix and Targeted Allocation of Plan Assets
The mix and targeted allocation of the pension and OPEB plans’ assets are as follows:
2026Assets at
TargetSeptember 30,
Asset AllocationAllocation20252024
U.S. equity securities29 %30 %29 %
International equity securities16 16 16 
Fixed income39 37 38 
Collective investment trusts at NAV16 17 17 
Total100 %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)202620272028202920302031 - 2035
Pension$17,309 $18,452 $19,506 $20,678 $21,625 $120,947 
OPEB$12,262 $13,511 $14,599 $15,620 $16,479 $89,419 
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 TypesDescription of the Valuation Methodologies
Money Market fundsRepresents bank balances and money market funds that are valued based on the NAV of shares held at year end.
Registered Investment CompaniesEquity 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 trustsThe 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.