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Assets and Liabilities Measured at Fair Value (Tables) | 3 Months Ended
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Mar. 31, 2025
Fair Value Disclosures [Abstract] |
Schedule of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis | The following tables present the Company's financial assets and liabilities measured at fair value on a recurring basis, as of March 31, 2025 and December 31, 2024:
|  | March 31, 2025
(Millions of dollars) |  | Level 1 |  | Level 2 |  | Level 3 |  | Fair Value
Financial assets |  |  |  |  |  |  |  |
Prepaid expenses and other current assets: |  |  |  |  |  |  |  |
Fuel derivative |  | $ | — |  |  | $ | — |  |  | $ | 0.2 |  |  | $ | 0.2 |
Other assets |  |  |  |  |  |  |  |
Deferred compensation plan assets |  | 15.2 |  |  | — |  |  | — |  |  | 15.2 |
Financial liabilities |  |  |  |  |  |  |  |
Deferred credits and other liabilities |  |  |  |  |  |  |  |
Deferred compensation plan liabilities |  | (25.8) |  |  | — |  |  | — |  |  | (25.8) |
|  | $ | (10.6) |  |  | $ | — |  |  | $ | 0.2 |  |  | $ | (10.4) |
|  | December 31, 2024
(Millions of dollars) |  | Level 1 |  | Level 2 |  | Level 3 |  | Fair Value
Financial assets |  |  |  |  |  |  |  |
Prepaid expenses and other current assets: |  |  |  |  |  |  |  |
Fuel derivative |  | $ | — |  |  | $ | — |  |  | $ | 0.2 |  |  | $ | 0.2 |
Other assets |  |  |  |  |  |  |  |
Deferred compensation plan assets |  | 14.9 |  |  | — |  |  | — |  |  | 14.9 |
Financial liabilities |  |  |  |  |  |  |  |
Deferred credits and other liabilities |  |  |  |  |  |  |  |
Deferred compensation plan liabilities |  | (26.3) |  |  | — |  |  | — |  |  | (26.3) |
|  | $ | (11.4) |  |  | $ | — |  |  | $ | 0.2 |  |  | $ | (11.2) |
Schedule of Carrying Amounts and Estimated Fair Value of Financial Instruments | The following table presents the carrying amounts and estimated fair values of financial instruments held by the Company at March 31, 2025 and December 31, 2024.
|  | At March 31, 2025 |  | At December 31, 2024
(Millions of dollars) |  | Carrying Amount |  | Fair Value |  | Carrying Amount |  | Fair Value
Financial liabilities |  |  |  |  |  |  |  |
Current and long-term debt, excluding finance leases |  | $ | (1,872.7) |  |  | $ | (1,867.2) |  |  | $ | (1,728.7) |  |  | $ | (1,717.5) |

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- Definition Tabular disclosure of the fair value of financial instruments, including financial assets and financial liabilities, and the measurements of those instruments, assets, and liabilities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 11 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482907/825-10-50-11 + Details
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- Definition Tabular disclosure of assets and liabilities, including [financial] instruments measured at fair value that are classified in stockholders' equity, if any, that are measured at fair value on a recurring basis. The disclosures contemplated herein include the fair value measurements at the reporting date by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 + Details
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