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Income Taxes - Roll-forward of Unrecognized Tax Benefits and Associated Accrued Interest and Penalties (Detail) - USD ($) $ in Millions | 9 Months Ended |
--- | --- | ---
Sep. 30, 2023 | Dec. 31, 2022
Income Tax Contingency [Line Items] |  |
Opening balance at January 1 | $ 13.4 |
Net change for tax positions of prior periods | 0.7 |
Closing balance at September 30 | 14.1 |
Current | 0.0 |
Non-current | 14.1 | $ 13.4
Interest and Penalties [Member] |  |
Income Tax Contingency [Line Items] |  |
Opening balance at January 1 | 3.2 |
Net change for tax positions of prior periods | 0.7 |
Closing balance at September 30 | 3.9 |
Current | 0.0 |
Non-current | 3.9 |
Unrecognized Tax Benefits [Member] |  |
Income Tax Contingency [Line Items] |  |
Opening balance at January 1 | 10.2 |
Net change for tax positions of prior periods | 0.0 |
Closing balance at September 30 | 10.2 |
Current | 0.0 |
Non-current | $ 10.2 |

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