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Business and Basis of Presentation Background and Business Description - Additional Information (Details) $ in Thousands | 9 Months Ended |
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Sep. 30, 2025 USD ($) level3FinancialInstruments | Dec. 31, 2024 USD ($)
Background And Basis Of Presentation [Line Items] |  |
Entity Incorporation, Date of Incorporation | Apr. 29, 1991 |
Number of Admitted Carriers Owned | 5 |
Number of Reportable Segments | 2 |
Short-Term Debt | $ | $ 0 | $ 150,000
Background and Business Description | 1. BACKGROUND AND BUSINESS DESCRIPTION Business The following description provides an update of Note 1. Background and Business Description and Note 2. Basis of Presentation and Significant Accounting Policies in the Notes to the Consolidated Financial Statements included in Part II, Item 8 in the Company’s Annual Report on Form 10-K for the year ended December 31, 2024, and should be read in conjunction with the complete descriptions provided in the Form 10-K. Capitalized terms used, but not defined herein, and in the other footnotes to the Consolidated Financial Statements included in this Quarterly Report on Form 10-Q shall have the meanings ascribed thereto in the Company’s Annual Report on Form 10-K for the year ended December 31, 2024. Ambac Financial Group, Inc. (“AFG”), headquartered in New York City, is an insurance holding company incorporated in the state of Delaware on April 29, 1991. References to “Ambac,” the “Company,” “we,” “our,” and “us” are to AFG and its subsidiaries, as the context requires. Ambac's principal businesses include: •Insurance Distribution — Ambac's specialty property and casualty ("P&C") insurance underwriting and distribution business, includes Managing General Agents and Underwriters (collectively "MGAs" or "MGA/Us"), an insurance broker, and other distribution and underwriting businesses. On October 31, 2025, the Company completed the acquisition of ArmadaCorp Capital, LLC and its subsidiaries (collectively, "ArmadaCare"), a leading specialty accident and health MGA. Ambac's insurance distribution platform operates in the following lines of business: property, niche specialty risk, accident & health, miscellaneous specialty, reinsurance, surety, marine & energy, specialty auto, other professional and professional Directors & Officers ("D&O") . •Specialty Property & Casualty Insurance — Ambac's Specialty Property & Casualty Insurance program business currently includes five carriers (collectively, “Everspan”). Everspan carriers have an A.M. Best rating of 'A-' (Excellent) which was last affirmed on July 17, 2025. The Company reports these two business operations as segments; see Note 2. Segment Information for further information. |

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- Definition The entire disclosure for the business description and basis of presentation concepts. Business description describes the nature and type of organization including but not limited to organizational structure as may be applicable to holding companies, parent and subsidiary relationships, business divisions, business units, business segments, affiliates and information about significant ownership of the reporting entity. Basis of presentation describes the underlying basis used to prepare the financial statements (for example, US Generally Accepted Accounting Principles, Other Comprehensive Basis of Accounting, IFRS). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 235 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 4 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483426/235-10-50-4 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 205 -Name Accounting Standards Codification -Publisher FASB -URI https://asc.fasb.org/205/tableOfContent + Details
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