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Regulatory Information - Narrative (Details) - USD ($) $ in Thousands |  | 3 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | --- | ---
Jun. 02, 2025 | Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024 | Dec. 31, 2025 | Dec. 31, 2024
NMIC and Re One combined |  |  |  |  |  |  |
Statutory Accounting Practices [Line Items] |  |  |  |  |  |  |
Net income amount |  | $ 30,700 | $ 20,000 | $ 98,000 | $ 90,700 |  |
Statutory capital |  | 3,143,710 |  | 3,143,710 |  |  | $ 2,890,352
Payments of ordinary dividends | $ 98,400 |  |  |  |  |  |
NMIC and Re One combined | Forecast |  |  |  |  |  |  |
Statutory Accounting Practices [Line Items] |  |  |  |  |  |  |
Aggregate dividend capacity |  |  |  |  |  | $ 98,400 |
Re One |  |  |  |  |  |  |
Statutory Accounting Practices [Line Items] |  |  |  |  |  |  |
Statutory capital |  | $ 2,100 |  | $ 2,100 |  |  | $ 2,100

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