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Reinsurance - Excess of Loss Reinsurance (Details) $ in Thousands |  |  |  |  |  |  |  |  | 9 Months Ended | 12 Months Ended
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Apr. 01, 2024 USD ($) | Oct. 23, 2023 USD ($) | Apr. 01, 2023 USD ($) | Apr. 26, 2022 USD ($) | Apr. 01, 2022 USD ($) | Aug. 03, 2021 USD ($) | Feb. 02, 2021 USD ($) | May 25, 2019 USD ($) | Sep. 30, 2024 USD ($) | Dec. 31, 2023 USD ($)
2024 Traditional XOL |  |  |  |  |  |  |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |  |  |  |  |  |  |
Amortization period excess of loss reinsurance coverage | 10 years |  |  |  |  |  |  |  |  |
Excess of loss reinsurance coverage, initial and remaining | $ 187,000 |  |  |  |  |  |  |  |  |
2023 Traditional XOL |  |  |  |  |  |  |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |  |  |  |  |  |  |
Amortization period excess of loss reinsurance coverage |  |  | 10 years |  |  |  |  |  |  |
Excess of loss reinsurance coverage, initial and remaining |  |  | $ 96,942 |  |  |  |  |  | $ 92,768 | $ 96,942
Initial First Layer Retention |  |  | $ 70,578 |  |  |  |  |  |  |
Remaining First Layer Retention |  |  |  |  |  |  |  |  | 70,516 | 70,578
2022 Traditional XOL |  |  |  |  |  |  |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |  |  |  |  |  |  |
Amortization period excess of loss reinsurance coverage |  |  |  |  | 10 years |  |  |  |  |
Excess of loss reinsurance coverage, initial and remaining |  |  |  |  | $ 142,642 |  |  |  | 129,315 | 142,642
Initial First Layer Retention |  |  |  |  | $ 82,523 |  |  |  |  |
Remaining First Layer Retention |  |  |  |  |  |  |  |  | $ 81,653 | 82,346
Excess of Loss Reinsurance Transactions, Home Re Transactions |  |  |  |  |  |  |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |  |  |  |  |  |  |
Percent of reinsurance coverage threshold, option to terminate (as a percent) |  |  |  |  |  |  |  |  | 10.00% |
Home Re 2023-1 |  |  |  |  |  |  |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |  |  |  |  |  |  |
Term of mortgage insurance-linked notes |  | 10 years |  |  |  |  |  |  |  |
Excess of loss reinsurance coverage, initial and remaining |  | $ 330,277 |  |  |  |  |  |  | $ 316,783 | 330,277
Initial First Layer Retention |  | $ 272,961 |  |  |  |  |  |  |  |
Remaining First Layer Retention |  |  |  |  |  |  |  |  | $ 272,633 | 272,961
Reinsurance Retention Policy, Funding Percentage |  | 0.97 |  |  |  |  |  |  | 0.97 |
Home Re 2022-1 |  |  |  |  |  |  |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |  |  |  |  |  |  |
Term of mortgage insurance-linked notes |  |  |  | 12 years 6 months |  |  |  |  |  |
Excess of loss reinsurance coverage, initial and remaining |  |  |  | $ 473,575 |  |  |  |  | $ 330,904 | 420,731
Initial First Layer Retention |  |  |  | $ 325,589 |  |  |  |  |  |
Remaining First Layer Retention |  |  |  |  |  |  |  |  | $ 323,269 | 325,001
Reinsurance Retention Policy, Funding Percentage |  |  |  | 1 |  |  |  |  | 1 |
Home Re 2021-2 |  |  |  |  |  |  |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |  |  |  |  |  |  |
Term of mortgage insurance-linked notes |  |  |  |  |  | 12 years 6 months |  |  |  |
Excess of loss reinsurance coverage, initial and remaining |  |  |  |  |  | $ 398,429 |  |  | $ 145,737 | 173,960
Initial First Layer Retention |  |  |  |  |  | $ 190,159 |  |  |  |
Remaining First Layer Retention |  |  |  |  |  |  |  |  | $ 188,803 | 189,403
Reinsurance Retention Policy, Funding Percentage |  |  |  |  |  | 1 |  |  | 0.82 |
Home Re 2021-1 |  |  |  |  |  |  |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |  |  |  |  |  |  |
Term of mortgage insurance-linked notes |  |  |  |  |  |  | 12 years 6 months |  |  |
Excess of loss reinsurance coverage, initial and remaining |  |  |  |  |  |  | $ 398,848 |  | $ 110,373 | 117,982
Initial First Layer Retention |  |  |  |  |  |  | $ 211,159 |  |  |
Remaining First Layer Retention |  |  |  |  |  |  |  |  | $ 210,303 | 210,831
Reinsurance Retention Policy, Funding Percentage |  |  |  |  |  |  | 1 |  | 1 |
Home Re 2019-1 |  |  |  |  |  |  |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |  |  |  |  |  |  |
Term of mortgage insurance-linked notes |  |  |  |  |  |  |  | 10 years |  |
Excess of loss reinsurance coverage, initial and remaining |  |  |  |  |  |  |  | $ 315,739 | $ 21,039 | 21,039
Initial First Layer Retention |  |  |  |  |  |  |  | $ 185,730 |  |
Remaining First Layer Retention |  |  |  |  |  |  |  |  | $ 182,220 | $ 182,722
Reinsurance Retention Policy, Funding Percentage |  |  |  |  |  |  |  | 1 | 0.10 |

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- Definition Reinsurance Agreement, Optional Call Feature, Right To Terminate, Percent Of Reinsurance Coverage Threshold + References No definition available. + Details
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- Definition Amount per life of risk undertaken originally by insurer that is not ceded to reinsurer. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479838/944-20-50-3 + Details
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