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Loss reserves - Summary of Liability For Unpaid Claims And Claim Adjustment Expenses (Details) - USD ($) $ in Thousands | Mar. 31, 2025 | Dec. 31, 2024 | Mar. 31, 2024 | Dec. 31, 2023
--- | --- | --- | --- | ---
Effects of Reinsurance [Line Items] |  |  |  |
Loss reserves | $ 542,528 | $ 524,715 |  |
Domestic mortgage insurance |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |
Loss reserves | 537,480 | 520,032 | $ 530,770 | $ 517,515
Other reserves |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |
Loss reserves | $ 5,048 | $ 4,683 |  |

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