DISCONTINUED OPERATION - Net Income (Loss) from Discontinued Operations (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2025	Sep. 30, 2025	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2021
EXPENSES:
Net income (loss) from discontinued operations			$ (163,288)	$ (497,167)	$ 28,183
Net income (loss) attributable to Ambac common shareholders			(163,288)	(497,167)	$ 28,183
Ambac Assurance Corporation | Discontinued Operations, Held-for-Sale or Disposed of by Sale
REVENUES:
Net premiums earned			15,145	23,879		$ 26,040
Net investment income			100,203	133,933		126,957
Net investment gains (losses), including impairments			(12,616)	4,416		(22,507)
Net gains (losses) on derivative contracts			302	3,958		(699)
Other revenues			18,016	31,096		14,533
Total revenues			121,050	197,282		144,324
EXPENSES:
Loss and loss adjustment expenses (benefit)			10,444	(45,767)		(69,320)
Intangible amortization			17,097	30,508		24,736
General & administrative and other expenses			81,034	57,491		88,306
Interest expense			47,617	63,587		64,025
Total expenses			156,192	105,819		107,747
Pretax income (loss)			(35,142)	91,463		36,577
Provision for income taxes			10,678	18,485		8,394
Discontinued Operation, Income (Loss) from Discontinued Operation During Phase-out Period, Net of Tax		$ (117,468)	(117,468)
Loss on disposal	$ 570,145	$ 687,613		(570,145)		0
Net income (loss) from discontinued operations			$ (163,288)	$ (497,167)		$ 28,183