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, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]
Liability for Claims and Claims Adjustment Expense	$ 373,105	$ 349,062
Liability for Claims	373,105	349,062
Ceded Loss And Loss Expenses Paid Not Yet Recovered			$ 15,088
Short-Duration Insurance Contracts, Liability for Unpaid Claims and Allocated Claim Adjustment Expense, Net	78,185
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	294,920	$ 270,081	$ 182,892	$ 156,232
Specialty Property & Casualty Program
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	294,920
Operating Segments | Specialty Property & Casualty Program
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]
Liability for Claims and Claims Adjustment Expense	373,105
Liability for Claims	373,105
Operating Segments | Commercial Auto
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]
Liability for Claims and Claims Adjustment Expense	155,383
Liability for Claims	155,383
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	127,775
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	27,608
Operating Segments | Excess and General Liability
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]
Liability for Claims and Claims Adjustment Expense	65,845
Liability for Claims	65,845
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	56,775
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	9,070
Operating Segments | Workers' Compensation Insurance
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]
Liability for Claims and Claims Adjustment Expense	14,602
Liability for Claims	14,602
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	14,602
Operating Segments | Non-standard Personal Auto
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]
Liability for Claims and Claims Adjustment Expense	9,149
Liability for Claims	9,149
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	396
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	8,753
Operating Segments | General Liability
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]
Liability for Claims and Claims Adjustment Expense	44,208
Liability for Claims	44,208
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	35,157
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	9,051
Operating Segments | Professional Liability Insurance
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]
Liability for Claims and Claims Adjustment Expense	23,373
Liability for Claims	23,373
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	21,561
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	1,812
Operating Segments | Surety Product Line
Financial Guarantee Insurance Contracts, Claim Liability [Line Items]
Liability for Claims and Claims Adjustment Expense	10,558
Liability for Claims	10,558
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	10,558
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	13,159
Liability for Claims	13,159
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	6,668
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	6,491
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	36,828
Liability for Claims	36,828
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	36,030
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	$ 798