v3.26.1
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