Consolidated Balance Sheets - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2025	Jun. 30, 2025	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Assets:
Debt Securities, Available-for-Sale	$ 264,055	$ 264,055
Total investments (net of allowance for credit losses of $0 and $0)	292,248	292,248		$ 312,915
Restricted Cash	23,841	23,841		17,669
Premiums Receivable, Net	71,875	71,875		57,222
Premium Receivable, Allowance for Credit Loss	200	200		142
Reinsurance Recoverables, Including Reinsurance Premium Paid	376,445	376,445		306,191
Deferred ceded premium	155,582	155,582		148,300
Intangible assets, less accumulated amortization	353,904	353,904		344,775
Goodwill	451,808	451,808		418,234	$ 69,694
Other assets	99,698	99,698		92,317
Disposal Group, Including Discontinued Operation, Net Assets Held-For Sale	6,592,417	6,592,417
Total assets	8,522,386	8,522,386		8,058,378
Liabilities:
Unearned premiums	191,060	191,060		182,446
Liability for Claims and Claims Adjustment Expense	383,969	383,969		349,062
Ceded premiums payable	90,557	90,557		53,002
Accrued interest payable	2,944	2,944		2,560
Derivative Liability	0	0		317
Other liabilities	95,900	95,900		89,036
Total liabilities	7,303,678	7,303,678		6,862,857
Redeemable Noncontrolling Interest, Equity, Redemption Value	190,347	190,347
Redeemable Noncontrolling Interest, Equity, Carrying Amount	190,347	190,347		140,860	17,079
Liabilities	7,303,678	7,303,678		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		0
Common Stock, Value, Issued	489	489		489
Additional paid-in capital	347,939	347,939		331,007
Accumulated other comprehensive income	(66,013)	(66,013)		(188,436)	(160,046)
Retained earnings	607,548	607,548		742,185
Treasury stock, shares at cost: 0 and 8,202	(30,124)	(30,124)		(28,339)
Total Ambac Financial Group, Inc. stockholders’ equity	859,839	859,839		856,906
Noncontrolling interest	168,522	168,522		197,755
Total stockholders’ equity	1,028,361	1,028,361		1,054,661	1,414,615
Total liabilities and stockholders’ equity	8,522,386	8,522,386		8,058,378
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0		0
Debt Securities, Available-for-sale, Amortized Cost	265,902	265,902		289,712
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	46,383	46,383		47,275	$ 19,223
Deferred Policy Acquisition Cost	9,407	9,407		8,572
Capitalized Contract Cost, Net	7,346	7,346		7,500
Deferred Income Tax Liabilities, Net	$ 72,003	$ 72,003		$ 70,135
Treasury Stock, Common, Shares	2,475,146	2,475,146		2,368,194
Preferred Stock, Shares Issued	0	0		0
Short-Term Debt	$ 150,000	$ 150,000		$ 150,000
Receivables, Net, Current	72,619	72,619	$ 55,377
Reinsurance Recoverable, Allowance for Credit Loss	100	100		100
Disposal Group, Including Discontinued Operation, Assets	6,636,855	6,636,855	6,267,200
Accrued Liabilities for Commissions, Expense and Taxes	96,875	96,875	71,431
Disposal Group, Including Discontinued Operation, Liabilities	6,213,024	6,213,024	$ 5,887,685
Afg [Member]
Stockholders’ equity:
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	46,383	46,383		47,275
Short-term Investments [Member]
Assets:
Debt Securities, Available-for-Sale	102,720	102,720		127,601
Stockholders’ equity:
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0		0
Debt Securities, Available-for-sale, Amortized Cost	102,719	102,719		127,588
Fixed Income Securities [Member]
Assets:
Debt Securities, Available-for-Sale	161,335	161,335		157,020
Stockholders’ equity:
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0		0
Debt Securities, Available-for-sale, Amortized Cost	163,183	163,183		162,124
Debt Securities, Available-for-Sale, Excluding Accrued Interest	161,335	161,335		157,020
Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss	163,183	163,183		162,124
Short-term Investments [Member]
Assets:
Debt Securities, Available-for-Sale	102,720	102,720		127,601
Stockholders’ equity:
Gross Investment Income, Operating	1,191	2,648
Other Investments [Member]
Stockholders’ equity:
Other Investment Not Readily Marketable, Fair Value	28,193	28,193		$ 28,294
Fixed Income Securities, Trading
Stockholders’ equity:
Gross Investment Income, Operating	$ 0	$ (79)