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Insurance Contracts - Summary of Information Related to Policies Currently Included in Ambac's Loss Reserves or Subrogation Recoverable (Phantom) (Details) - USD ($) $ in Thousands | Jun. 30, 2025 | Dec. 31, 2024 | Jun. 30, 2024 | Dec. 31, 2023
--- | --- | --- | --- | ---
Financial Guarantee Insurance Contracts, Claim Liability [Line Items] |  |  |  |
Liability for Claims and Claims Adjustment Expense | $ 383,969 | $ 349,062 |  |
Liability for Claims | 383,969 | 349,062 |  |
Ceded Loss And Loss Expenses Paid Not Yet Recovered |  |  | $ 35,146 |
Short-Duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net | 78,556 |  |  |
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | 305,414 | $ 270,081 | $ 215,490 | $ 156,301
Specialty Property & Casualty Program |  |  |  |
Financial Guarantee Insurance Contracts, Claim Liability [Line Items] |  |  |  |
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | 305,414 |  |  |
Operating Segments | Specialty Property & Casualty Program |  |  |  |
Financial Guarantee Insurance Contracts, Claim Liability [Line Items] |  |  |  |
Liability for Claims and Claims Adjustment Expense | 383,969 |  |  |
Liability for Claims | 383,969 |  |  |
Operating Segments | Commercial Auto |  |  |  |
Financial Guarantee Insurance Contracts, Claim Liability [Line Items] |  |  |  |
Liability for Claims and Claims Adjustment Expense | 148,616 |  |  |
Liability for Claims | 148,616 |  |  |
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | 123,361 |  |  |
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 | 25,255 |  |  |
Operating Segments | Excess and General Liability |  |  |  |
Financial Guarantee Insurance Contracts, Claim Liability [Line Items] |  |  |  |
Liability for Claims and Claims Adjustment Expense | 74,404 |  |  |
Liability for Claims | 74,404 |  |  |
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | 63,632 |  |  |
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 | 10,772 |  |  |
Operating Segments | Workers' Compensation Insurance |  |  |  |
Financial Guarantee Insurance Contracts, Claim Liability [Line Items] |  |  |  |
Liability for Claims and Claims Adjustment Expense | 16,604 |  |  |
Liability for Claims | 16,604 |  |  |
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 | 16,604 |  |  |
Operating Segments | Non-standard Personal Auto |  |  |  |
Financial Guarantee Insurance Contracts, Claim Liability [Line Items] |  |  |  |
Liability for Claims and Claims Adjustment Expense | 7,051 |  |  |
Liability for Claims | 7,051 |  |  |
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | 395 |  |  |
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 | 6,656 |  |  |
Operating Segments | General Liability |  |  |  |
Financial Guarantee Insurance Contracts, Claim Liability [Line Items] |  |  |  |
Liability for Claims and Claims Adjustment Expense | 52,081 |  |  |
Liability for Claims | 52,081 |  |  |
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | 41,653 |  |  |
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 | 10,428 |  |  |
Operating Segments | Professional Liability Insurance |  |  |  |
Financial Guarantee Insurance Contracts, Claim Liability [Line Items] |  |  |  |
Liability for Claims and Claims Adjustment Expense | 27,853 |  |  |
Liability for Claims | 27,853 |  |  |
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | 25,833 |  |  |
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 | 2,020 |  |  |
Operating Segments | Surety Product Line |  |  |  |
Financial Guarantee Insurance Contracts, Claim Liability [Line Items] |  |  |  |
Liability for Claims and Claims Adjustment Expense | 12,250 |  |  |
Liability for Claims | 12,250 |  |  |
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | 12,250 |  |  |
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 | 0 |  |  |
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 | 14,066 |  |  |
Liability for Claims | 14,066 |  |  |
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | 8,168 |  |  |
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 | 5,898 |  |  |
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 | 31,044 |  |  |
Liability for Claims | 31,044 |  |  |
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments | 30,122 |  |  |
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 | $ 922 |  |  |

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