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Retirement Plan and Other Post-Retirement Benefits - Schedule of Cumulative Amounts Recognized in AOCI (Loss) and Regulatory Assets and Liabilities (Details) $ in Thousands | 12 Months Ended
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Sep. 30, 2025 USD ($) | [1]
Non-Qualified Benefit Plans |  |
Amounts Recognized in Accumulated Other Comprehensive Income (Loss), Regulatory Assets and Regulatory Liabilities |  |
Net Actuarial Loss | $ (13,353) |
Prior Service (Cost) Credit | 0 |
Net Amount Recognized | (13,353) |
Changes to Accumulated Other Comprehensive Income (Loss), Regulatory Assets and Regulatory Liabilities |  |
Increase in Actuarial Loss, excluding amortization | (1,061) | [2]
Change due to Amortization of Actuarial Loss | 1,101 |
Prior Service (Cost) Credit | 0 |
Net Change | 40 |
Retirement Plan | Qualified Plan |  |
Amounts Recognized in Accumulated Other Comprehensive Income (Loss), Regulatory Assets and Regulatory Liabilities |  |
Net Actuarial Loss | (178,675) |
Prior Service (Cost) Credit | (1,372) |
Net Amount Recognized | (180,047) |
Changes to Accumulated Other Comprehensive Income (Loss), Regulatory Assets and Regulatory Liabilities |  |
Increase in Actuarial Loss, excluding amortization | (20,828) | [2]
Change due to Amortization of Actuarial Loss | 6,481 |
Prior Service (Cost) Credit | 302 |
Net Change | (14,045) |
Other Post-Retirement Benefits | Qualified Plan |  |
Amounts Recognized in Accumulated Other Comprehensive Income (Loss), Regulatory Assets and Regulatory Liabilities |  |
Net Actuarial Loss | (19,813) |
Prior Service (Cost) Credit | 257 |
Net Amount Recognized | (19,556) |
Changes to Accumulated Other Comprehensive Income (Loss), Regulatory Assets and Regulatory Liabilities |  |
Increase in Actuarial Loss, excluding amortization | (19,722) | [2]
Change due to Amortization of Actuarial Loss | 37 |
Prior Service (Cost) Credit | (429) |
Net Change | $ (20,114) |
[1] | Amounts presented are shown before recognizing deferred taxes.
[2] | Amounts presented include the impact of actuarial gains/losses related to return on assets, as well as the Actuarial Loss amounts presented in the Change in Benefit Obligation.

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- Definition Changes To Accumulated Other Comprehensive Income (Loss), Regulatory Assets and Regulatory Liabilities + References No definition available. + Details
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- Definition The pretax total of net (gain) loss, prior service cost (credit), and transition assets (obligations), as well as minimum pension liability if still remaining, included in accumulated other comprehensive income or regulatory assets and regulatory liabilities associated with a defined benefit pension or other postretirement plan(s) because they have yet to be recognized as components of net periodic benefit cost. + References No definition available. + Details
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- Definition The pretax net amount of gains and losses that are not yet recognized as a component of net periodic benefit cost, and that are recognized as increases or decreases in other comprehensive income or regulatory assets and regulatory liabilities as they arise. Gains and losses are due to changes in the value of either the benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption, or the consequence of a decision to temporarily deviate from the substantive plan. + References No definition available. + Details
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- Definition Amount related to the pretax cost of benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation, which has not yet been recognized as components of net periodic benefit cost. + References No definition available. + Details
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- Definition The pretax cost (credit) of benefit changes attributable to plan participants' prior service resulting from a plan amendment or plan initiation that occurred during the period. The cost has not yet been recognized in net periodic benefit cost. A plan amendment includes provisions that grant increased (decreased) benefits based on services rendered in prior periods. + References No definition available. + Details
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- Definition Amounts recognized in other comprehensive income (but not yet recognized in net periodic benefit cost), including the net gain (loss) and net prior service cost (credit), or regulatory assets and regulatory liabilities arising during the period. Also includes reclassification adjustments out of other comprehensive income as a result of being recognized as components of net periodic benefit cost for the period. + References No definition available. + Details
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- Definition Pretax change in the value of either the benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption, or the consequence of a decision to temporarily deviate from the substantive plan, that has not been recognized in net periodic benefit cost. + References No definition available. + Details
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- Definition Before tax amount of the income statement impact or change in regulatory assets and regulatory liabilities of the reclassification adjustment for actuarial gain (loss) recognized as a component of net periodic benefit cost. + References No definition available. + Details
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