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v3.25.1

Investments - Summary of Gross Unrealized Losses and Fair Values of Ambac's Available-for-Sale Investments (Details) $ in Thousands | Dec. 31, 2025 USD ($) | Mar. 31, 2025 USD ($) | Dec. 31, 2024 USD ($)
--- | --- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  |  | $ 792
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer |  | $ 60,829 | 68,012
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 3,735 | 4,559
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | $ 5,351 | 3,994 | 5,351
DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss, including pledged securities |  | 259 |
Debt Securities , Available for sale, Continuous Unrealized Loss Position, |  | 24,475 | 51,012
Debt Securities, Available for sale, Unrealized Loss Position, Including Pledged Securities |  |  | 119,024
Short-term Investments [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 0 | 0 |
Fixed Income Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 5,351 | 3,994 |
Fixed Income Securities [Member] | Municipal Bonds [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months |  | 2,070 | 6,042
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | 35 | 112
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer |  | 6,660 | 6,582
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 373 | 458
Debt Securities, Available-for-sale, Unrealized Loss Position |  | 8,730 | 12,624
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 570 | 408 | 570
Fixed Income Securities [Member] | Corporate Debt Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months |  | 9,782 | 23,784
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | 135 | 269
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer |  | 42,021 | 46,612
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 3,018 | 3,636
Debt Securities, Available-for-sale, Unrealized Loss Position |  | 51,803 | 70,396
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 3,905 | $ 3,153 | 3,905
Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions |  | 136,000 |
Fixed Income Securities [Member] | Debt Security, Government, Non-US [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months |  | $ 0 | 0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | 0 | 0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer |  | 0 | 0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 0 | 0
Debt Securities, Available-for-sale, Unrealized Loss Position |  | 0 | 0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax |  | 0 | 0
Fixed Income Securities [Member] | US Government Debt Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months |  | 6,704 | 15,919
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | 46 | 344
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer |  | 12,148 | 14,818
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 344 | 465
Debt Securities, Available-for-sale, Unrealized Loss Position |  | 18,852 | 30,737
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 809 | 390 | 809
Fixed Income Securities [Member] | Residential Mortgage-Backed Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months |  | 1,899 | 2,446
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | 18 | 29
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer |  | 0 | 0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 0 | 0
Debt Securities, Available-for-sale, Unrealized Loss Position |  | 1,899 | 2,446
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 29 | 18 | 29
Fixed Income Securities [Member] | Commercial Mortgage Backed Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months |  | 750 | 738
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | 22 | 34
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer |  | 0 | 0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 0 | 0
Debt Securities, Available-for-sale, Unrealized Loss Position |  | 750 | 738
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax |  | 22 | 34
Fixed Income Securities [Member] | Collateralized Debt Obligations [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months |  | 654 | 655
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | 1 | 2
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer |  | 0 | 0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 0 | 0
Debt Securities, Available-for-sale, Unrealized Loss Position |  | 654 | 655
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 2 | 1 | 2
Fixed Income Securities [Member] | Asset-backed Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months |  | 848 | 1,428
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | 2 | 2
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer |  | 0 | 0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 0 | 0
Debt Securities, Available-for-sale, Unrealized Loss Position |  | 848 | 1,428
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | $ 2 | $ 2 | $ 2

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