Consolidated Balance Sheets - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2025	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Assets:
Fixed maturity securities, at fair value	$ 263,179
Total investments (net of allowance for credit losses of $0 and $0)	291,393		$ 312,915
Restricted Cash	17,596		17,669
Premiums Receivable, Net	64,563		57,222
Premium Receivable, Allowance for Credit Loss	142		142
Reinsurance Recoverables, Including Reinsurance Premium Paid	351,110		306,191
Deferred ceded premium	144,914		148,300
Derivative assets	210		0
Intangible assets, less accumulated amortization	345,061		344,775
Goodwill	429,314		418,234	$ 69,694
Other assets	107,829		92,317
Total assets	8,253,282		8,058,378
Liabilities:
Unearned premiums	181,387		182,446
Liability for Claims and Claims Adjustment Expense	373,105		349,062
Ceded premiums payable	81,358		53,002
Accrued interest payable	2,695		2,560
Derivative Liability	0		317
Other liabilities	91,429		89,036
Total liabilities	7,041,817		6,862,857
Redeemable Noncontrolling Interest, Equity, Redemption Value	185,417
Redeemable Noncontrolling Interest, Equity, Carrying Amount	185,417		140,860	17,079
Liabilities	7,041,817		6,862,857
Stockholders’ equity:
Preferred stock, par value $0.01 per share; 20,000,000 shares authorized; issued and outstanding shares—none	0		0
Common Stock, Value, Issued	489		489
Additional paid-in capital	333,356		331,007
Accumulated other comprehensive income	(133,168)		(188,436)	(160,046)
Retained earnings	681,489		742,185
Treasury stock, shares at cost: 0 and 8,202	(29,945)		(28,339)
Total Ambac Financial Group, Inc. stockholders’ equity	852,221		856,906
Noncontrolling interest	173,827		197,755
Total stockholders’ equity	1,026,048		1,054,661	1,414,615
Total liabilities and stockholders’ equity	8,253,282		8,058,378
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	$ 0	0
Debt Securities, Available-for-sale, Amortized Cost	266,292	289,712
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	51,660		47,275	$ 19,223
Deferred Policy Acquisition Cost	9,615		8,572
Capitalized Contract Cost, Net	7,176		7,500
Deferred Income Tax Liabilities, Net	$ 69,742		$ 70,135
Treasury Stock, Common, Shares	2,447,746		2,368,194
Preferred Stock, Shares Issued	0		0
Short-Term Debt	$ 150,000		$ 150,000
Receivables, Net, Current	65,819	55,377
Reinsurance Recoverable, Allowance for Credit Loss	100		100
Disposal Group, Including Discontinued Operation, Assets	6,392,004	6,267,200
Accrued Liabilities for Commissions, Expense and Taxes	81,017	71,431
Disposal Group, Including Discontinued Operation, Liabilities	6,003,908	5,887,685
Afg [Member]
Stockholders’ equity:
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	51,660		47,275
Short-term Investments [Member]
Assets:
Fixed maturity securities, at fair value	101,610	127,601
Stockholders’ equity:
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Debt Securities, Available-for-sale, Amortized Cost	101,604	127,588	127,588
Fixed Income Securities [Member]
Assets:
Fixed maturity securities, at fair value	161,569	157,020
Stockholders’ equity:
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Debt Securities, Available-for-sale, Amortized Cost	164,688	$ 162,124
Debt Securities, Available-for-Sale, Excluding Accrued Interest	161,569		157,020
Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss	164,688		162,124
Short-term Investments [Member]
Assets:
Fixed maturity securities, at fair value	101,610		127,601
Stockholders’ equity:
Gross Investment Income, Operating	1,457
Other Investments [Member]
Stockholders’ equity:
Other Investment Not Readily Marketable, Fair Value	28,214		$ 28,294
Gross Investment Income, Operating	$ (79)