Consolidated Balance Sheets - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2024	Dec. 31, 2023	Dec. 31, 2022
Assets:
Fixed maturity securities, at fair value	$ 2,073,000	$ 2,073,000
Total investments (net of allowance for credit losses of $1 and $3)	2,634,000	2,634,000	$ 2,664,000
Restricted Cash	16,000	16,000	12,000
Premiums Receivable, Net	342,000	342,000	290,000
Premium Receivable, Allowance for Credit Loss	3,000	3,000	4,000
Reinsurance Recoverables on Unpaid Losses, Allowance	0	0	0
Reinsurance Recoverables, Including Reinsurance Premium Paid	311,000	311,000	195,000
Deferred ceded premium	242,000	242,000	204,000
Subrogation recoverable	124,000	124,000	137,000
Derivative assets	33,000	33,000	26,000
Intangible assets, less accumulated amortization	598,000	598,000	307,000
Goodwill	434,000	434,000	70,000	$ 61,000
Other assets	228,000	228,000	129,000
Total assets	9,256,000	9,256,000	8,428,000
Liabilities:
Unearned premiums	458,000	458,000	422,000
Liability for Claims and Claims Adjustment Expense	938,000	938,000	893,000
Ceded premiums payable	165,000	165,000	90,000
Long-term debt	518,000	518,000	508,000
Accrued interest payable	515,000	515,000	475,000
Derivative Liability	35,000	35,000	35,000
Other liabilities	262,000	262,000	180,000
Total liabilities	7,383,000	7,383,000	6,997,000
Redeemable Noncontrolling Interest, Equity, Redemption Value	204,000	204,000
Redeemable Noncontrolling Interest, Equity, Carrying Amount	204,000	204,000	17,000	20,000
Liabilities	7,383,000	7,383,000	6,997,000
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	0	0	0
Additional paid-in capital	328,000	328,000	292,000
Accumulated other comprehensive income	(81,000)	(81,000)	(160,000)	(253,000)
Retained earnings	1,235,000	1,235,000	1,246,000
Treasury stock, shares at cost: 0 and 8,202	(17,000)	(17,000)	(17,000)
Total Ambac Financial Group, Inc. stockholders’ equity	1,465,000	1,465,000	1,362,000
Noncontrolling interest	205,000	205,000	53,000
Total stockholders’ equity	1,670,000	1,670,000	1,415,000	1,305,000
Total liabilities and stockholders’ equity	9,256,000	9,256,000	8,428,000
Debt Securities, Available-for-sale, Allowance for Credit Loss	1,000	1,000	3,000
Debt Securities, Available-for-sale, Amortized Cost	2,069,000	2,069,000	2,197,000
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	117,000	117,000	274,000	$ 61,000
Deferred Policy Acquisition Cost	13,000	13,000	11,000
Capitalized Contract Cost, Net	8,000	8,000	6,000
Deferred Income Tax Liabilities, Net	$ 100,000	$ 100,000	$ 19,000
Treasury Stock, Common, Shares	1,432,634	1,432,634	1,463,774
Preferred Stock, Shares Issued	0	0	0
Short-Term Debt	$ 148,000	$ 148,000
Afg [Member]
Stockholders’ equity:
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	70,000	70,000	$ 28,000
Short-term Investments [Member]
Assets:
Fixed maturity securities, at fair value	305,000	305,000	426,000
Stockholders’ equity:
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0	0
Debt Securities, Available-for-sale, Amortized Cost	305,000	305,000	426,000
Variable Interest Entity, Primary Beneficiary [Member]
Assets:
Fixed maturity securities, at fair value	2,238,000	2,238,000	2,167,000
Restricted Cash	47,000	47,000	246,000
Derivative assets	216,000	216,000	226,000
Other assets	110,000	110,000	92,000
Total assets	4,262,000	4,262,000	4,394,000
Liabilities:
Long-term debt	2,996,000	2,996,000	2,967,000
Derivative Liability	1,223,000	1,223,000	1,197,000
Other Sundry Liabilities, Current	51,000	51,000	240,000
Other liabilities	10,000	10,000	5,000
Total liabilities	4,271,000	4,271,000	4,404,000
Liabilities	4,271,000	4,271,000	4,404,000
Stockholders’ equity:
Financing Receivable, after Allowance for Credit Loss	1,651,000	1,651,000	1,663,000
Gross Investment Income, Operating	3,000
Derivative and other assets	326,000	326,000	318,000
Fixed Income Securities [Member]
Assets:
Fixed maturity securities, at fair value	1,740,000	1,740,000	1,710,000
Stockholders’ equity:
Debt Securities, Available-for-sale, Allowance for Credit Loss	1,000	1,000	3,000
Debt Securities, Available-for-sale, Amortized Cost	1,737,000	1,737,000	1,744,000
Debt Securities, Available-for-Sale, Excluding Accrued Interest	1,740,000	1,740,000	1,710,000
Debt Securities, Available-for-Sale, Amortized Cost, Excluding Accrued Interest, before Allowance for Credit Loss	1,737,000	1,737,000	1,744,000
Short-term Investments [Member]
Assets:
Fixed maturity securities, at fair value	305,000	305,000	426,000
Stockholders’ equity:
Gross Investment Income, Operating	4,000	14,000
Other Investments [Member]
Stockholders’ equity:
Other Investment Not Readily Marketable, Fair Value	561,000	561,000	475,000
Gross Investment Income, Operating	14,000	35,000
Fixed Income Securities, Trading
Stockholders’ equity:
Gross Investment Income, Operating	0	4,000
Debt Securities, Available-for-Sale, Excluding Accrued Interest	0	0	27,000
Collateral Pledged [Member] | Fixed Income Securities [Member]
Assets:
Fixed maturity securities, at fair value	27,000	27,000	27,000
Stockholders’ equity:
Debt Securities, Available-for-sale, Amortized Cost	27,000	27,000	0
Collateral Pledged [Member] | Fixed Income Securities [Member] | Short-term Investments [Member]
Assets:
Fixed maturity securities, at fair value	0	0	27,000
Stockholders’ equity:
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0	0
Debt Securities, Available-for-sale, Amortized Cost	0	0	27,000
Collateral Pledged [Member] | Short-term Investments
Stockholders’ equity:
Debt Securities, Available-for-sale, Amortized Cost	0	0	27,000
Collateralized Securities | Fixed Income Securities [Member]
Stockholders’ equity:
Debt Securities, Available-for-Sale, Excluding Accrued Interest	27,000	27,000	0
Collateralized Securities | Short-term Investments [Member]
Assets:
Fixed maturity securities, at fair value	$ 0	$ 0	$ 27,000