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Insurance Contracts - Additional Information (Details) $ in Thousands, € in Millions, £ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Sep. 30, 2024 USD ($) | Sep. 30, 2023 USD ($) | Sep. 30, 2024 USD ($) | Sep. 30, 2023 USD ($) | Dec. 31, 2023 USD ($) | Sep. 30, 2024 GBP (£) | Sep. 30, 2024 EUR (€) | Jun. 30, 2024 USD ($) | Sep. 30, 2023 GBP (£) | Sep. 30, 2023 EUR (€) | Jun. 30, 2023 USD ($) | Dec. 31, 2022 USD ($)
Insurance [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Reinsurance Recoverable Credit Exposure | $ 200,000 |  | $ 200,000 |  | $ 128,000 |  |  |  |  |  |  |
Estimated Future Premium Payments Weighted Average Discounted Rate | 3.10% |  | 3.10% |  | 3.20% | 3.10% | 3.10% |  |  |  |  |
Reinsurance Payable | $ 165,000 |  | $ 165,000 |  | $ 90,000 |  |  |  |  |  |  |
Weighted average period of future premiums |  |  | 7 years 4 months 24 days |  | 8 years |  |  |  |  |  |  |
Uncollectable premium receivables | 3,000 |  | $ 3,000 |  | $ 4,000 |  |  |  |  |  |  |
Reinsurance recoveries of losses included in losses and loss expenses |  |  | (74,000) | $ (75,000) |  |  |  |  |  |  |  |
Amortization of Intangible Assets | 13,000 | $ 7,000 | 33,000 | 21,000 |  |  |  |  |  |  |  |
Intangible assets, less accumulated amortization | 598,000 |  | 598,000 |  | 307,000 |  |  |  |  |  |  |
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest | 1,670,000 | 1,318,000 | 1,670,000 | 1,318,000 | $ 1,415,000 |  |  | $ 1,419,000 |  |  | $ 1,303,000 | $ 1,305,000
Past Due Premiums | 3,000 | 2,000 | $ 3,000 | $ 2,000 |  |  |  |  |  |  |  |
Loss Reserves [Member] |  |  |  |  |  |  |  |  |  |  |  |
Insurance [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Weighted average risk-free rate used to discount loss reserves |  |  | 3.80% | 4.60% |  |  |  |  |  |  |  |
United Kingdom, Pounds |  |  |  |  |  |  |  |  |  |  |  |
Insurance [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Financial Guarantee Insurance Contracts, Premium Receivable | 67,000 | 71,000 | $ 67,000 | $ 71,000 |  | £ 50 |  |  | £ 58 |  |  |
Euro Member Countries, Euro |  |  |  |  |  |  |  |  |  |  |  |
Insurance [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Financial Guarantee Insurance Contracts, Premium Receivable | $ 12,000 | $ 13,000 | $ 12,000 | $ 13,000 |  |  | € 11 |  |  | € 13 |  |

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- Definition Amount of the premium receivable for financial guarantee insurance contracts reported in the statement of financial position. This element primarily would consist of those financial guarantee insurance contracts which premiums are to be collected over the contract period, but may, on occasion, include premiums which are to be collected in full at inception, but which straddle a financial reporting period. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 310 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (c)(1) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479584/944-310-50-3 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 310 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (c)(5) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479584/944-310-50-3 + Details
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