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