Third-Party Reinsurance - Reinsurance Recoverables (Details) - P&C Insurance and Reinsurance (Ark/WM Outrigger) - USD ($) $ in Millions |
Sep. 30, 2026 |
Dec. 31, 2025 |
|---|---|---|
| Segment Reporting [Line Items] | ||
| Reinsurance recoverables on unpaid losses | $ 608.8 | $ 508.3 |
| Reinsurance recoverables on paid losses | 61.5 | 117.6 |
| Ceded unearned premiums | 405.8 | 210.2 |
| Reinsurance recoverables | 1,076.1 | 836.1 |
| Ark | ||
| Segment Reporting [Line Items] | ||
| Reinsurance recoverables on unpaid losses | (23.4) | (29.5) |
| Reinsurance recoverables on paid losses | (1.6) | (5.2) |
| Ceded unearned premiums | $ 0.0 | $ (3.9) |
| X | ||||||||||
- Definition The unexpired portion of premiums ceded on policies in force as of the balance sheet date. Reference 1: http://www.xbrl.org/2003/role/exampleRef
|
| X | ||||||||||
- Definition Amount, after valuation allowance, recoverable under reinsurance contracts for losses reported to the ceding insurer but not yet paid and amounts expected for incurred losses and settlement expenses, which have not yet been reported to the ceding insurer. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
|
| X | ||||||||||
- Definition Amount, after valuation allowance, recoverable under reinsurance contracts including premium paid under reinsurance contracts. Examples include, but are not limited to, settled and unsettled claims, incurred but not reported losses, loss adjustment expense, premium paid, policy benefits and policy reserves. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
|
| X | ||||||||||
- Definition Amount, after valuation allowance, recoverable under reinsurance contracts for losses reported to and paid by the ceding insurer. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
|
| X | ||||||||||
- 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
|
| X | ||||||||||
- Details
|
| X | ||||||||||
- Details
|