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Fair Value Measurements | 12 Months Ended
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Sep. 30, 2025
Fair Value Disclosures [Abstract] |
Fair Value Measurements | Fair Value Measurements We report certain assets and liabilities at fair value, which is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date (exit price). We record cash and cash equivalents and restricted cash and cash equivalents, accounts receivable, and accounts payable at carrying value, which substantially approximates fair value due to the short-term nature of these assets and liabilities. For other financial assets and liabilities, we primarily use quoted market prices and other observable market pricing information to minimize the use of unobservable pricing inputs in our measurements when determining fair value. The methods used to determine fair value for our assets and liabilities are fully described in Note 2 to the consolidated financial statements. Fair value measurements also apply to the valuation of our pension and postretirement plan assets. The fair value of these assets is presented in Note 11 to the consolidated financial statements. Quantitative Disclosures Financial Instruments The classification of our fair value measurements requires judgment regarding the degree to which market data are observable or corroborated by observable market data. The following tables summarize, by level within the fair value hierarchy, our assets and liabilities that were accounted for at fair value on a recurring basis as of September 30, 2025 and 2024. As required under authoritative accounting literature, assets and liabilities are categorized in their entirety based on the lowest level of input that is significant to the fair value measurement.
| Quoted Prices in Active Markets (Level 1) |  | Significant Other Observable Inputs (Level 2)(1) |  | Significant Other Unobservable Inputs (Level 3) |  | Netting and Cash Collateral |  | September 30, 2025
| (In thousands)
Assets: |  |  |  |  |  |  |  |  |
Financial instruments | $ | — |  |  | $ | 9,897 |  |  | $ | — |  |  | $ | — |  |  | $ | 9,897 |
Debt and equity securities |  |  |  |  |  |  |  |  |
Registered investment companies | 26,463 |  |  | — |  |  | — |  |  | — |  |  | 26,463 |
Bond mutual funds | 42,106 |  |  | — |  |  | — |  |  | — |  |  | 42,106 |
Bonds (2) | — |  |  | 42,754 |  |  | — |  |  | — |  |  | 42,754 |
Money market funds | — |  |  | 3,615 |  |  | — |  |  | — |  |  | 3,615 |
Total debt and equity securities | 68,569 |  |  | 46,369 |  |  | — |  |  | — |  |  | 114,938 |
Total assets | $ | 68,569 |  |  | $ | 56,266 |  |  | $ | — |  |  | $ | — |  |  | $ | 124,835 |
Liabilities: |  |  |  |  |  |  |  |  |
Financial instruments | $ | — |  |  | $ | 6,485 |  |  | $ | — |  |  | $ | — |  |  | $ | 6,485 |
| Quoted Prices in Active Markets (Level 1) |  | Significant Other Observable Inputs (Level 2)(1) |  | Significant Other Unobservable Inputs (Level 3) |  | Netting and Cash Collateral |  | September 30, 2024
| (In thousands)
Assets: |  |  |  |  |  |  |  |  |
Financial instruments | $ | — |  |  | $ | 96,288 |  |  | $ | — |  |  | $ | — |  |  | $ | 96,288 |
Debt and equity securities |  |  |  |  |  |  |  |  |
Registered investment companies | 28,311 |  |  | — |  |  | — |  |  | — |  |  | 28,311 |
Bond mutual funds | 40,341 |  |  | — |  |  | — |  |  | — |  |  | 40,341 |
Bonds (2) | — |  |  | 39,142 |  |  | — |  |  | — |  |  | 39,142 |
Money market funds | — |  |  | 2,800 |  |  | — |  |  | — |  |  | 2,800 |
Total debt and equity securities | 68,652 |  |  | 41,942 |  |  | — |  |  | — |  |  | 110,594 |
Total assets | $ | 68,652 |  |  | $ | 138,230 |  |  | $ | — |  |  | $ | — |  |  | $ | 206,882 |
Liabilities: |  |  |  |  |  |  |  |  |
Financial instruments | $ | — |  |  | $ | 7,637 |  |  | $ | — |  |  | $ | — |  |  | $ | 7,637 |
(1)Our Level 2 measurements consist of over-the-counter options and swaps, which are valued using a market-based approach in which observable market prices are adjusted for criteria specific to each instrument, such as the strike price, notional amount, or basis differences, municipal and corporate bonds, which are valued based on the most recent available quoted market prices and money market funds which are valued at cost. (2)Our investments in bonds are considered available-for-sale debt securities in accordance with current accounting guidance. Debt and equity securities are comprised of our available-for-sale debt securities and our equity securities. We evaluate the performance of our available-for-sale debt securities on an investment by investment basis for impairment, taking into consideration the investment’s purpose, volatility, current returns, and any intent to sell the security. As of September 30, 2025, no allowance for credit losses was recorded for our available-for-sale debt securities. At September 30, 2025 and 2024, the amortized cost of our available-for-sale debt securities was $42.5 million and $38.9 million. At September 30, 2025 we maintained investments in bonds that have contractual maturity dates ranging from October 2025 through January 2028. Other Fair Value Measures In addition to the financial instruments above, we have several financial and nonfinancial assets and liabilities subject to fair value measures. These financial assets and liabilities include cash and cash equivalents and restricted cash and cash equivalents, accounts receivable, accounts payable, finance leases, and debt, which are recorded at carrying value. The nonfinancial assets and liabilities include asset retirement obligations and pension and postretirement plan assets. For cash and cash equivalents and restricted cash and cash equivalents, accounts receivable, accounts payable, and finance leases we consider carrying value to materially approximate fair value due to the short-term nature of these assets and liabilities. Our long-term debt is recorded at carrying value. The fair value of our long-term debt, excluding finance leases, is determined using third party market value quotations, which are considered Level 1 fair value measurements for debt instruments with a recent, observable trade or Level 2 fair value measurements for debt instruments where fair value is determined using the most recent available quoted market price. The following table presents the carrying value and fair value of our long-term debt, excluding finances leases, debt issuance costs and original issue premium or discount, as of September 30, 2025:
| September 30, 2025
| (In thousands)
Carrying Amount | $ | 8,935,000 |
Fair Value | $ | 8,272,978 |

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- Definition The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (bbb)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 107 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482078/820-10-55-107 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 100 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482078/820-10-55-100 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (c)(3) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 6A -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-6A Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2E -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2E Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 6A -Subparagraph (h) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-6A Reference 8: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 6A -Subparagraph (f) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-6A Reference 9: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 6A -Subparagraph (e) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-6A Reference 10: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 6A -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-6A Reference 11: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (h) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 12: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (g) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 13: http://www.xbrl.org/2003/role/disclosureRef -Topic 940 -SubTopic 820 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478119/940-820-50-1 + Details
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