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Municipal Bond Guarantee Reinsurance - Narrative (Details) $ in Millions | 6 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Dec. 31, 2024 USD ($) | Dec. 31, 2024 USD ($) | Dec. 31, 2023 USD ($) | Dec. 31, 2022 USD ($) | Jul. 01, 2024 USD ($) | Jun. 30, 2024
Guarantor Obligations [Line Items] |  |  |  |  |  |
Member surplus contributions, insurance premium charges, percentage | 55.00% | 55.00% |  |  |  |
Direct written premiums |  | $ 56.0 | $ 58.6 | $ 65.1 |  |
Gross earned premiums |  | 31.7 | 31.2 | 33.3 |  |
Assets held-in-trust | $ 950.1 | 950.1 | 948.5 |  |  |
Distribution received |  | 79.7 |  |  |  |
Surplus notes distribution received |  | 58.5 |  |  |  |
Cash distribution received |  | 21.2 |  |  |  |
Collateral trusts, investments and cash | 289.4 | 289.4 | 247.0 |  |  |
Interest receivable | 7.7 | 7.7 | 37.7 |  |  |
Surplus notes | 300.9 | 300.9 | 322.2 |  |  |
Debt | 562.5 | 562.5 | 564.6 |  |  |
Change in fair value of BAM Surplus Notes |  | 0.5 | 0.0 | 0.0 |  |
Operating Segments | Financial Guarantee (HG Global) |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
Debt | 147.4 | 147.4 | 146.9 |  |  |
Notes receivable, fair value disclosure | 381.7 | 381.7 | 0.0 |  | $ 387.4 |
Change in fair value of BAM Surplus Notes |  | $ 0.5 | 0.0 | $ 0.0 |  |
BAM Surplus Notes | Surplus Notes |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
Basis spread on variable rate |  | 3.00% |  |  |  |
Interest rate |  |  |  |  | 10.00% | 8.20%
Cash repayments on notes |  | $ 30.0 | 27.4 |  |  |
Repayment of principal |  | 21.3 | 17.8 |  |  |
Accrued interest payment held in trust |  | 0.5 | 2.0 |  |  |
Accrued interest payment held outside of trust |  | 8.2 | 7.6 |  |  |
Debt | 300.9 | 300.9 | 322.2 |  |  |
Interest receivable | $ 194.8 | $ 194.8 | 174.5 |  |  |
BAM Surplus Notes | Surplus Notes | Discount Rate |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
Debt instrument, measurement input | 0.0810 | 0.0810 |  |  | 0.0815 |
Subsidiary - HG Global |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
Purchase of surplus notes |  | $ 503.0 |  |  |  |
Percentage of risk premium ceded | 60.00% | 60.00% |  |  |  |
Renegotiation period |  | 5 years |  |  |  |
Direct written premiums | $ 31.9 |  |  |  |  |
Gross earned premiums | 14.9 |  |  |  |  |
Percent over a target trust balance |  | 102.00% |  |  |  |
Subsidiary - HG Global | Regulation 114 |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
Assets held-in-trust | 352.1 | $ 352.1 | 341.6 |  |  |
Supplement trust target | 603.0 | 603.0 |  |  |  |
Subsidiary - HG Global | Supplemental Trust |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
Assets held-in-trust | $ 598.0 | $ 598.0 | $ 606.9 |  |  |
Subsidiary - HG Global | Maximum |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
Percentage of par value of policy reinsured | 15.00% | 15.00% |  |  |  |
Variable Interest Entity, Primary Beneficiary - Build America Mutual Assurance Company | Fidus Re Ltd. |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |
Reinsured amount |  | $ 125.0 |  |  |  |

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