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v3.25.3

Fair Value of Financial Instruments - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Millions | Sep. 30, 2025 | Dec. 31, 2024
--- | --- | ---
Assets: |  |
Investments | $ 16.8 | $ 14.4
Energy Marketing Contracts Assets, Current | 0.1 | 0.6
Liabilities: |  |
Energy Marketing Contract Liabilities, Current | 0.5 | 0.0
Quoted Prices in Active Markets (Level 1) [Member] |  |
Assets: |  |
Assets, Fair Value Disclosure | 15.9 | 13.3
Quoted Prices in Active Markets (Level 1) [Member] | Investments - Mutual funds and other [Member] |  |
Assets: |  |
Investments | 15.9 | 13.3
Quoted Prices in Active Markets (Level 1) [Member] | Total Investments [Member] |  |
Assets: |  |
Investments | 15.9 | 13.3
Significant Other Observable Inputs (Level 2) [Member] |  |
Assets: |  |
Assets, Fair Value Disclosure | 0.1 | 0.7
Significant Unobservable Inputs (Level 3) [Member] |  |
Assets: |  |
Assets, Fair Value Disclosure | 0.9 | 1.1
Significant Unobservable Inputs (Level 3) [Member] | Investments in guaranteed income fund [Member] |  |
Assets: |  |
Investments | 0.9 | 1.1
Significant Unobservable Inputs (Level 3) [Member] | Total Investments [Member] |  |
Assets: |  |
Investments | 0.9 | 1.1
Recurring [Member] |  |
Assets: |  |
Assets, Fair Value Disclosure | 16.9 | 15.1
Liabilities: |  |
Energy Marketing Contract Liabilities, Current |  | 0.1
Recurring [Member] | Investments in guaranteed income fund [Member] |  |
Assets: |  |
Investments | 0.9 | 1.1
Recurring [Member] | Investments - Mutual funds and other [Member] |  |
Assets: |  |
Investments |  | 13.3
Recurring [Member] | Total Investments [Member] |  |
Assets: |  |
Investments | 16.8 | 14.4
Recurring [Member] | Mark To Market Energy Assets incl. natural gas and swap agreements[Member] |  |
Assets: |  |
Derivative assets | $ 0.1 | $ 0.7

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- Definition Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. 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