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Summary of Significant Accounting Policies - Regulatory Liabilities (Detail) - USD ($) $ in Millions | Sep. 30, 2024 | Dec. 31, 2023 | Sep. 30, 2023
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Regulatory Liabilities [Line Items] |  |  |
Regulatory Liabilities | $ 68.7 | $ 47.9 | $ 51.7
Less: Current Portion of Regulatory Liabilities | 22.4 | 13.5 | 16.9
Regulatory Liabilities – noncurrent | 46.3 | 34.4 | 34.8
Income Taxes |  |  |
Regulatory Liabilities [Line Items] |  |  |
Regulatory Liabilities | 50.0 | 38.6 | 38.9
Rate Adjustment Mechanisms & Other |  |  |
Regulatory Liabilities [Line Items] |  |  |
Regulatory Liabilities | $ 18.7 | $ 9.3 | $ 12.8

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- Definition The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 980 -SubTopic 405 -Name Accounting Standards Codification -Section 25 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477571/980-405-25-1 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition The amount for the individual regulatory current liability as itemized in a table of regulatory current liabilities as of the end of the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 980 -SubTopic 405 -Name Accounting Standards Codification -Section 25 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477571/980-405-25-1 + Details
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- Definition The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(24)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1 + Details
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