Schedule II - Condensed Financial Information of Registrant (Parent Company Only) - Condensed Statement of Total Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Revenues:
Other revenue	$ 7,235	$ 6,422	$ (426)	$ 83	$ 67	$ (5)	$ 101	$ 37	$ 13,314	$ 200	$ 577
Net investment gains (losses), including impairments	4,455	577	(4,535)	0	(1)	0	20	(38)	497	(19)	62
Total revenues and other income									235,815	124,728	53,612
General and Administrative Expense	40,444	44,681	28,336	18,050	21,193	17,914	17,117	11,839	129,166	66,985	56,278
Expenses:
Income tax expense (benefit)									924	989	462
Net income (loss)	(548,265)	(27,504)	(750)	20,070	(15,688)	65,869	(13,132)	(33,417)	(556,088)	4,951	522,120
Other comprehensive income, after tax:
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Total	(20,943)	(19,890)	(14,719)	(3,369)	(9,099)	(4,595)	(8,725)	(813)	(58,921)	(23,232)	(35,244)
Unrealized gains (losses) on securities, net of deferred income taxes of $0									(939)	51,184	(225,341)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax									(22,156)	40,132	(84,520)
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Reclassification Adjustment from AOCI for Derecognition, after Tax									(356)	(88)	340
Total other comprehensive income (loss), net of income tax									(28,390)	92,797	(310,454)
Total comprehensive income (loss) attributable to Ambac shareholders									(581,765)	96,429	211,926
Net gains (losses) on derivative contracts	$ (2,043)	$ 6,545	$ (438)	$ (48)	$ 69	$ (27)	$ (146)	$ (175)	4,016	(279)	935
Parent Company [Member]
Condensed Income Statements, Captions [Line Items]
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax									1,295	2,095	(6,264)
Other Comprehensive Income (Loss), Foreign Currency Translation Gain (Loss) Arising During Period, Tax									0	0	0
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Reclassification Adjustment from AOCI for Derecognition, Tax									(118)	177	79
Revenues:
Investment income									7,262	9,298	10,389
Other revenue									(415)	6	(81)
Net investment gains (losses), including impairments									498	(55)	13,664
Total revenues and other income									10,259	9,011	(2,421)
General and Administrative Expense									41,519	21,597	17,435
Expenses:
Operating Expenses									41,519	21,597	17,435
Pretax income (loss) from continuing operations									(31,260)	(12,586)	(19,856)
Income tax expense (benefit)									1,748	1,193	462
Income (loss) before equity pick-up of net income (loss) of subsidiaries									29,512	11,393	19,394
Equity in undistributed net income (loss) of subsidiaries									(526,937)	15,026	541,773
Net income (loss)									(556,449)	3,633	522,379
Other comprehensive income, after tax:
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Total									(556,449)	3,632	522,380
Unrealized gains (losses) on securities, net of deferred income taxes of $0									(939)	51,184	(225,341)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax									(22,156)	40,132	(84,520)
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Reclassification Adjustment from AOCI for Derecognition, after Tax									(356)	(88)	340
Changes to postretirement benefit, net of tax									(4,939)	1,569	(933)
Total other comprehensive income (loss), net of income tax									(28,390)	92,797	(310,454)
Total comprehensive income (loss) attributable to Ambac shareholders									(584,839)	96,430	211,925
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Plan Amendments, Tax Effect									0	0	0
Net gains (losses) on derivative contracts									$ 3,910	$ (348)	$ 935