Schedule II - Condensed Financial Information of Registrant (Parent Company Only) - Condensed Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Condensed Balance Sheet Statements, Captions [Line Items]
Common stock, shares issued	48,875,167	46,659,144
Treasury Stock, Common, Shares	2,368,194	1,463,774
Common Stock, Shares, Outstanding	46,506,973
Assets:
Debt Securities, Available-for-sale	$ 157,020	$ 135,224
Short-term investments, at cost (approximates fair value)	289,712	341,685
Other Investments	28,294	18,317
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Investments, Total	312,915	354,051
Investment income due and accrued	1,703	1,569
Derivative assets	0	656
Other assets	92,317	65,817
Assets	8,058,378	8,428,320	$ 7,972,730
Liabilities:
Liabilities	6,862,857	6,996,627
Stockholders' equity (deficit):
Preferred Stock, Value, Issued	0	0
Common stock	489	467
Additional paid-in capital	331,007	291,761
Accumulated other comprehensive income (loss)	(188,436)	(160,047)	(252,843)
Retained earnings	742,185	1,246,048
Common stock held in treasury at cost	(28,339)	(16,573)
Total Ambac Financial Group, Inc. stockholders’ equity	856,906	1,361,656
Total liabilities, redeemable noncontrolling interest and stockholders’ equity	8,058,378	8,428,320
Short-term investments, amortized cost	127,588	200,506
Ambac Financial Group, Inc Parent Company Only [Member]
Assets:
Debt Securities, Available-for-sale	0	13,920
Short-term investments, at cost (approximates fair value)	0	14,045
Other Investments	28,117	18,317
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Investments, Total	92,556	187,925
Cash	9,981	250
Investment in subsidiaries	737,692	1,150,195
Investment income due and accrued	269	545
Other assets	22,703	26,258
Assets	863,201	1,365,173
Liabilities:
Accounts payable and other liabilities	6,294	3,515
Liabilities	6,294	3,515
Stockholders' equity (deficit):
Preferred Stock, Value, Issued	0	0
Common stock	489	467
Additional paid-in capital	331,007	291,761
Accumulated other comprehensive income (loss)	(188,436)	(160,046)
Retained earnings	742,185	1,246,049
Common stock held in treasury at cost	(28,339)	(16,573)
Total Ambac Financial Group, Inc. stockholders’ equity	856,906	1,361,658	$ 1,252,331	$ 1,038,105
Total liabilities, redeemable noncontrolling interest and stockholders’ equity	863,201	1,365,173
Short-term investments, amortized cost	64,439	155,687
Short-term Investments [Member]
Assets:
Debt Securities, Available-for-sale	127,601	200,510
Short-term investments, at cost (approximates fair value)	127,588	200,506
Debt Securities, Available-for-sale, Allowance for Credit Loss	0	0
Short-term Investments [Member] | Ambac Financial Group, Inc Parent Company Only [Member]
Assets:
Short-term investments, at cost (approximates fair value)	$ 64,439	$ 155,688