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Investments - Summary of Amortized Cost and Estimated Fair Value of Available-for-Sale Investments, Excluding VIE Investments Held by Successor Ambac, by Contractual Maturity (Details) - USD ($) $ in Thousands | Dec. 31, 2025 | Mar. 31, 2025
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Debt Securities, Available-for-sale, Amortized Cost | $ 289,712 | $ 266,292
Fixed maturity securities, at fair value |  | 263,179
Amortized Cost, Due in one year or less |  | 135,653
Amortized Cost, Due after one year through five years |  | 58,649
Amortized Cost, Due after five years through ten years |  | 57,785
Amortized Cost, Due after ten years |  | 977
Amortized Cost, Total |  | 253,064
Estimated Fair Value, Due in one year or less |  | 135,297
Estimated Fair Value, Due after one year through five years |  | 57,690
Estimated Fair Value, Due after five years through ten years |  | 55,980
Estimated Fair Value, Due after ten years |  | 977
Estimated Fair Value due, Total |  | 249,944
Fixed Income Securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Debt Securities, Available-for-sale, Amortized Cost | 162,124 | 164,688
Fixed maturity securities, at fair value | 157,020 | 161,569
Fixed Income Securities [Member] | Residential Mortgage-Backed Securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Debt Securities, Available-for-sale, Amortized Cost | 2,475 | 3,447
Fixed maturity securities, at fair value | 2,446 | 3,445
Fixed Income Securities [Member] | Commercial Mortgage Backed Securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Debt Securities, Available-for-sale, Amortized Cost |  | 2,067
Fixed maturity securities, at fair value |  | 2,049
Fixed Income Securities [Member] | Collateralized Debt Obligations [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Debt Securities, Available-for-sale, Amortized Cost | 3,131 | 2,941
Fixed maturity securities, at fair value | 3,142 | 2,954
Fixed Income Securities [Member] | Asset-backed Securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Debt Securities, Available-for-sale, Amortized Cost | 5,049 | 4,773
Fixed maturity securities, at fair value | $ 5,061 | $ 4,787

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