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Debt and Credit Facility (Tables) | 9 Months Ended
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Sep. 30, 2025
Debt Disclosure [Abstract] |
Summary of Senior Notes | The following table summarizes key details of our Senior Notes:
|  |  |  |  |  | Outstanding (in millions of dollars) |
|  | Issuance Date |  | Maturity |  | Effective Interest Rate |  | As of September 30, 2025 |  |  | As of December 31, 2024 |
4.625% Senior Notes |  | November 2019 |  | March 2028 |  | 4.8% |  | $ | 500.0 |  |  | $ | 500.0 |
4.50% Senior Notes |  | May 2021 |  | June 2031 |  | 4.7% |  |  | 550.0 |  |  |  | 550.0 |
Total debt |  |  |  |  |  |  |  |  | 1,050.0 |  |  |  | 1,050.0 |
Unamortized issuance costs |  |  |  |  |  |  |  |  | (7.1 | ) |  |  | (8.4 | )
Total carrying amount |  |  |  |  |  |  |  | $ | 1,042.9 |  |  | $ | 1,041.6 |
Summary of Fair Value of Outstanding Senior Notes | The following table presents the fair value of our outstanding Senior Notes, which are Level 1 liabilities (in millions of dollars):
|  |  |  |  |  | As of September 30, 2025 |  |  | As of December 31, 2024 |
4.625% Senior Notes |  |  |  |  |  | $ | 494.4 |  |  | $ | 470.1 |
4.50% Senior Notes |  |  |  |  |  | $ | 518.4 |  |  | $ | 484.8 |
Schedule of Availability and Usage of Revolving Credit Facility | The following table summarizes availability and usage of our Revolving Credit Facility as determined by a borrowing base calculated as of September 30, 2025 (in millions of dollars):
Revolving Credit Facility borrowing commitment |  | $ | 575.0 |
Borrowing base availability |  | $ | 575.0 |
Less: Outstanding borrowings under Revolving Credit Facility |  |  | — |
Less: Outstanding letters of credit under Revolving Credit Facility |  |  | (14.6 | )
Remaining borrowing availability |  | $ | 560.4 |
Summary of Interest Expense Relating to Senior Notes and Revolving Credit Facility | The following table presents interest expense relating to our Senior Notes and Revolving Credit Facility (in millions of dollars):
|  | Quarter Ended September 30, |  |  | Nine Months Ended September 30, |
|  | 2025 |  |  | 2024 |  |  | 2025 |  |  | 2024 |
Senior Notes interest expense, including debt issuance cost amortization |  | $ | 12.4 |  |  | $ | 12.4 |  |  | $ | 37.2 |  |  | $ | 37.2 |
Revolving Credit Facility interest expense, including commitment fees and finance cost amortization |  |  | 0.7 |  |  |  | 0.6 |  |  |  | 2.0 |  |  |  | 1.8 |
Interest expense on finance lease liabilities |  |  | 0.2 |  |  |  | 0.2 |  |  |  | 0.6 |  |  |  | 0.6 |
Interest expense capitalized as construction in progress |  |  | (0.9 | ) |  |  | (2.5 | ) |  |  | (3.7 | ) |  |  | (6.3 | )
Total interest expense |  | $ | 12.4 |  |  | $ | 10.7 |  |  | $ | 36.1 |  |  | $ | 33.3 |

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