v3.26.1
Insurance Contracts - Summary of Information Related to Policies Currently Included in Ambac's Loss Reserves or Subrogation Recoverable (Phantom) (Details) - USD ($)
$ in Thousands
Mar. 31, 2026
Dec. 31, 2025
Mar. 31, 2025
Dec. 31, 2024
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]        
Liability for Claims and Claims Adjustment Expense $ 487,261 $ 459,990    
Liability for Claims 487,261 459,990    
Ceded Loss And Loss Expenses Paid Not Yet Recovered     $ 56,190  
Short-Duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net 95,908      
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments 391,352 $ 375,722 $ 294,920 $ 270,081
Specialty Property & Casualty Program        
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]        
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments 391,352      
Operating Segments | Specialty Property & Casualty Program        
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]        
Liability for Claims and Claims Adjustment Expense 487,261      
Liability for Claims 487,261      
Operating Segments | Commercial Auto        
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]        
Liability for Claims and Claims Adjustment Expense 162,853      
Liability for Claims 162,853      
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments 133,407      
Operating Segments | Commercial Auto | Specialty Property & Casualty Program        
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]        
Short-Duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net 29,446      
Operating Segments | Excess and General Liability        
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]        
Liability for Claims and Claims Adjustment Expense 128,381      
Liability for Claims 128,381      
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments 109,617      
Operating Segments | Excess and General Liability | Specialty Property & Casualty Program        
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]        
Short-Duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net 18,764      
Operating Segments | Workers' Compensation Insurance        
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]        
Liability for Claims and Claims Adjustment Expense 19,752      
Liability for Claims 19,752      
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments 0      
Operating Segments | Workers' Compensation Insurance | Specialty Property & Casualty Program        
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]        
Short-Duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net 19,752      
Operating Segments | Non-standard Personal Auto        
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]        
Liability for Claims and Claims Adjustment Expense 2,895      
Liability for Claims 2,895      
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments 191      
Operating Segments | Non-standard Personal Auto | Specialty Property & Casualty Program        
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]        
Short-Duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net 2,704      
Operating Segments | General Liability        
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]        
Liability for Claims and Claims Adjustment Expense 62,391      
Liability for Claims 62,391      
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments 49,641      
Operating Segments | General Liability | Specialty Property & Casualty Program        
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]        
Short-Duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net 12,750      
Operating Segments | Professional Liability Insurance        
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]        
Liability for Claims and Claims Adjustment Expense 48,219      
Liability for Claims 48,219      
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments 44,831      
Operating Segments | Professional Liability Insurance | Specialty Property & Casualty Program        
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]        
Short-Duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net 3,388      
Operating Segments | Surety Product Line        
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]        
Liability for Claims and Claims Adjustment Expense 10,767      
Liability for Claims 10,767      
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments 9,707      
Operating Segments | Surety Product Line | Specialty Property & Casualty Program        
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]        
Short-Duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net 1,060      
Operating Segments | Multi-peril        
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]        
Liability for Claims and Claims Adjustment Expense 11,246      
Liability for Claims 11,246      
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments 8,918      
Operating Segments | Multi-peril | Specialty Property & Casualty Program        
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]        
Short-Duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net 2,328      
Segment Reporting, Reconciling Item, Excluding Corporate Nonsegment | Unallocated Loss Adjustment Expense Reserve        
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]        
Liability for Claims and Claims Adjustment Expense 15,515      
Liability for Claims 15,515      
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments 9,969      
Segment Reporting, Reconciling Item, Excluding Corporate Nonsegment | Unallocated Loss Adjustment Expense Reserve | Specialty Property & Casualty Program        
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]        
Short-Duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net 5,546      
Segment Reporting, Reconciling Item, Excluding Corporate Nonsegment | Other Insurance Contracts        
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]        
Liability for Claims and Claims Adjustment Expense 25,242      
Liability for Claims 25,242      
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments 25,071      
Segment Reporting, Reconciling Item, Excluding Corporate Nonsegment | Other Insurance Contracts | Specialty Property & Casualty Program        
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]        
Short-Duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net $ 171