Schedule II - Condensed Financial Information of Registrant (Parent Company Only) - Condensed Statements of Cash Flows (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
Cash flows from operating activities:
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)
Adjustments to reconcile net income loss to net cash used in operating activities:
Amortization of bond premium and discount									(296)	9	(6,742)
Net investment gains (losses), including impairments	4,455	$ 577	$ (4,535)	0	(1)	$ 0	$ 20	(38)	497	(19)	62
Share-based compensation									9,356	12,266	11,231
Proceeds from Contributions from Affiliates									10,739	8,032	5,760
Other, net									237	(7,819)	37,260
Net Cash Provided by (Used in) Investing Activities [Abstract]
Proceeds from matured bonds									21,580	15,078	18,097
Purchases of bonds									(60,470)	(33,243)	(43,489)
Change in short-term investments									101,829	4,157	(48,386)
Proceeds from Sale and Maturity of Other Investments									625
Other, net									(3,750)	(4,854)	2,329
Cash flows from financing activities:
Cash and cash equivalents at beginning of period				7,342				6,329	7,342	6,329
Cash and cash equivalents end of period	29,606				7,342				29,606	7,342	6,329
Cash paid during the period for:
Income taxes									526	381	347
Payments to Acquire Businesses, Net of Cash Acquired									243,776	6,953	18,442
Payments for Repurchase of Common Stock									11,698	4,510	14,217
Stock Issued During Period, Value, Acquisitions									29,229	0	0
Ambac Financial Group, Inc Parent Company Only [Member]
Cash flows from operating activities:
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Total									(556,449)	3,632	522,380
Adjustments to reconcile net income loss to net cash used in operating activities:
Equity in undistributed net (income) loss of non-debtor subsidiaries									526,937	(15,027)	(541,773)
Amortization of bond premium and discount									0	0	(7,378)
Net investment gains (losses), including impairments									498	(55)	13,664
Decrease in current income taxes payable									(1,970)	(1,674)	(809)
Share-based compensation									8,361	9,404	11,962
Decrease in other assets									7,817	(4,660)	40,976
Other, net									1,814	2,392	1,109
Net cash provided by (used in) operating activities									(1,755)	2,044	45,891
Net Cash Provided by (Used in) Investing Activities [Abstract]
Proceeds from matured bonds									5,000	0	68,205
Purchases of bonds									0	(795)	(750)
Change in short-term investments									91,249	19,676	(51,069)
Proceeds from Sale and Maturity of Other Investments									(1,749)	(2,715)	(4,213)
Net Cash Provided by (Used in) Investing Activities, Total									94,500	16,166	12,173
Capital Contribution to Subsidiaries									(70,817)	(16,050)	(42,420)
Cash flows from financing activities:
Net Cash Provided by (Used in) Financing Activities									(82,516)	(20,560)	(56,637)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Excluding Exchange Rate Effect									9,731	(2,350)	1,427
Cash and cash equivalents at beginning of period				$ 250				$ 2,600	250	2,600	1,173
Cash and cash equivalents end of period	$ 9,981				$ 250				9,981	250	2,600
Cash paid during the period for:
Income taxes									0	0	0
Payments for Repurchase of Common Stock									(11,699)	(4,510)	(14,217)
Stock Issued During Period, Value, Acquisitions									$ 29,229	$ 0	$ 0