v3.26.1
Investments - Summary of Gross Unrealized Losses and Fair Values of Ambac's Available-for-Sale Investments (Details)
$ in Thousands
Jun. 30, 2026
USD ($)
level3FinancialInstruments
Dec. 31, 2025
USD ($)
Debt Securities, Available-for-sale [Line Items]    
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss   $ 48
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer $ 34,680 47,658
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 2,232 2,268
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax 2,951 2,316
Debt Securities, Available for sale, Unrealized Loss Position, Including Pledged Securities   52,969
DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss, including pledged securities 719  
Debt Securities , Available for sale, Continuous Unrealized Loss Position, $ 60,988 5,311
Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions | level3FinancialInstruments 186  
Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions | level3FinancialInstruments 100  
Municipal Bonds [Member]    
Debt Securities, Available-for-sale [Line Items]    
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months $ 1,194 535
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 14 16
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer 4,575 5,820
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 187 212
Debt Securities, Available-for-sale, Unrealized Loss Position 5,769 6,355
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax 201 228
Corporate Debt Securities [Member]    
Debt Securities, Available-for-sale [Line Items]    
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months 25,390 1,807
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 299 10
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer 24,024 30,751
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 1,956 1,932
Debt Securities, Available-for-sale, Unrealized Loss Position 49,414 32,558
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax $ 2,255 1,942
Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions | level3FinancialInstruments 126  
Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions | level3FinancialInstruments 64  
Largest Individual Unrealized Loss as a Percentage of Amortized Cost 11.80%  
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 $ 30,226 2,206
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 353 14
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer 4,724 9,491
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 76 117
Debt Securities, Available-for-sale, Unrealized Loss Position 34,950 11,697
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax 429 131
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 1,070 0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 11 0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer 1,357 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 2,427 1,596
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax 24 7
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 2,515 763
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 41 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 2,515 763
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax 41 8
Collateralized Debt Obligations [Member]    
Debt Securities, Available-for-sale [Line Items]    
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months 593 0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 1 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 593 0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax 1 0
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
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