Investments - Summary of Gross Unrealized Losses and Fair Values of Ambac's Available-for-Sale Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 40,146	$ 5,311
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	441	48
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	39,782	47,658
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2,305	2,268
Debt Securities, Available-for-sale, Unrealized Loss Position	79,928	52,969
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	2,746	2,316
DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss, including pledged securities	441
Debt Securities , Available for sale, Continuous Unrealized Loss Position,	40,146	5,311
Debt Securities, Available for sale, Unrealized Loss Position, Including Pledged Securities		52,969
Short-term Investments [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 Investments And Other Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	2,746
Fixed Income Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	40,146	5,311
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	441	48
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	39,782	47,658
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2,305	2,268
Debt Securities, Available-for-sale, Unrealized Loss Position	79,928	52,969
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	2,746	2,316
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	532	535
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	20	16
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	4,904	5,820
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	197	212
Debt Securities, Available-for-sale, Unrealized Loss Position	5,436	6,355
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	217	228
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	22,033	1,807
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	249	10
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	26,654	30,751
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2,000	1,932
Debt Securities, Available-for-sale, Unrealized Loss Position	48,687	32,558
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	2,249	1,942
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	14,522	2,206
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	124	14
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	6,770	9,491
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	94	117
Debt Securities, Available-for-sale, Unrealized Loss Position	21,292	11,697
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	218	131
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	473	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	8	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	1,454	1,596
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	13	7
Debt Securities, Available-for-sale, Unrealized Loss Position	1,927	1,596
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	21	7
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	2,518	763
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	40	8
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	2,518	763
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	40	8
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	68	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	1	0
Debt Securities, Available-for-sale, Unrealized Loss Position	68	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1	0
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	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

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