Cash, cash equivalents, restricted cash and restricted investments (Details) - USD ($) $ in Millions |
Sep. 30, 2026 |
Dec. 31, 2025 |
Sep. 30, 2025 |
Dec. 31, 2024 |
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| Restricted Cash and Cash Equivalent Item [Line Items] | ||||
| Cash and cash equivalents | $ 434.3 | $ 731.2 | ||
| Restricted cash | 127.4 | 171.2 | ||
| Total cash, cash equivalents and restricted cash | 561.7 | 902.4 | $ 717.7 | $ 894.6 |
| Restricted investments securing reinsurance contracts and letter of credit facilities | 1,733.1 | 2,040.7 | ||
| Total cash, cash equivalents, restricted cash and restricted investments | 2,294.8 | 2,943.1 | ||
| Managing general underwriters | ||||
| Restricted Cash and Cash Equivalent Item [Line Items] | ||||
| Restricted cash | 14.4 | 12.8 | ||
| Letter of credit facilities | ||||
| Restricted Cash and Cash Equivalent Item [Line Items] | ||||
| Restricted cash | 23.0 | 69.1 | ||
| Reinsurance contracts | ||||
| Restricted Cash and Cash Equivalent Item [Line Items] | ||||
| Restricted cash | $ 90.0 | $ 89.3 |
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- Definition Cash, Cash Equivalents, Restricted Cash, Restricted Cash Equivalents And Restricted Investments No definition available.
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- Definition Amount of cash and cash equivalent. Cash includes, but is not limited to, currency on hand, demand deposit with financial institution, and account with general characteristic of demand deposit. Cash equivalent includes, but is not limited to, short-term, highly liquid investment that is both readily convertible to known amount of cash and so near maturity that it presents insignificant risk of change in value because of change in interest rate. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount of cash and cash equivalent, and cash and cash equivalent restricted to withdrawal or usage; attributable to continuing operation. Cash includes, but is not limited to, currency on hand, demand deposit with financial institution, and account with general characteristic of demand deposit. Cash equivalent includes, but is not limited to, short-term, highly liquid investment that is both readily convertible to known amount of cash and so near maturity that it presents insignificant risk of change in value because of change in interest rate. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Amount of cash and cash equivalent restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposit with financial institution, and account with general characteristic of demand deposit. Cash equivalent includes, but is not limited to, short-term, highly liquid investment that is both readily convertible to known amount of cash and so near maturity that it presents insignificant risk of change in value because of change in interest rate. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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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. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition Investments which are not defined as or included in marketable (debt, equity, or other) securities whose use is restricted in whole or in part, generally by contractual agreements or regulatory requirements. For use in an unclassified balance sheet. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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