Debt and letter of credit facilities - Debt Obligations (Details) - USD ($) $ in Millions |
Sep. 30, 2026 |
Dec. 31, 2025 |
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| Debt Instrument [Line Items] | ||
| Total debt | $ 667.5 | $ 688.6 |
| Subordinated Notes | ||
| Debt Instrument [Line Items] | ||
| Debt, at face value | 275.6 | 298.2 |
| Unamortized discount | (5.0) | (5.6) |
| Total debt | $ 270.6 | $ 292.6 |
| Effective rate | 6.20% | 7.10% |
| 2024 Senior Notes | Senior Notes | ||
| Debt Instrument [Line Items] | ||
| Debt, at face value | $ 400.0 | $ 400.0 |
| Unamortized discount and issuance costs | (3.1) | (4.0) |
| Total debt | $ 396.9 | $ 396.0 |
| Effective rate | 7.40% | 7.40% |
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- Definition Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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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/2003/role/disclosureRef
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- Definition Amount, after accumulated amortization, of debt discount. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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