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Income Taxes - Significant Components of Deferred Tax Liabilities and Assets (Details) - USD ($) $ in Thousands | Sep. 30, 2025 | Sep. 30, 2024
--- | --- | ---
Deferred Tax Liabilities: |  |
Unrealized Hedging Gains | $ 9,036 | $ 22,433
Property, Plant and Equipment | 1,222,869 | 1,134,727
Pension and Other Post-Retirement Benefit Costs | 72,691 | 59,877
Other | 24,531 | 13,885
Total Deferred Tax Liabilities | 1,329,127 | 1,230,922
Deferred Tax Assets: |  |
Tax Loss and Credit Carryforwards | (28,364) | (31,111)
Pension and Other Post-Retirement Benefit Costs | (54,071) | (49,622)
Other | (21,430) | (39,024)
Total Deferred Tax Assets | (103,865) | (119,757)
Total Net Deferred Income Taxes | $ 1,225,262 | $ 1,111,165

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- Definition The cumulative amount of the estimated future tax effects attributable to pension and other post-retirement benefit costs not otherwise specified in this taxonomy that were expensed for tax purposes but capitalized in conformity with generally accepted accounting principles, or which were recognized as revenue under GAAP but not for tax purposes, which will reverse in future periods. + References No definition available. + Details
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- Definition The cumulative amount of the estimated future tax effects attributable to pension and other post-retirement benefit costs not otherwise specified in this taxonomy that were expensed for tax purposes but capitalized in conformity with generally accepted accounting principles, or which were recognized as revenue under GAAP but not for tax purposes, which will reverse in future periods. + References No definition available. + Details
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- Definition Amount after allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482685/740-10-50-2 + Details
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