Consolidated Statements of Total Comprehensive Income - Successor [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues:
Net premiums earned	$ 30,883	$ 47,613
Net investment income:
Securities available-for-sale and short-term	110,551	73,150
Other investments	(311)	8,409
Total net investment income	110,240	81,559
Other-than-temporary impairment losses:
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities	(341)	(21,154)
Portion of other-than-temporary impairment recognized in other comprehensive income	42	17,212
Net other-than-temporary impairments	(299)	(3,942)
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments	4,862	(4,896)
Change in fair value of credit derivatives:
Gain (Loss) on Sale of Derivatives	106	199
Unrealized gains (losses)	(452)	853
Net change in fair value of credit derivatives	(346)	1,052
Net gains (losses) on interest rate derivatives	25,537	(1,514)
Net realized gains (losses) on extinguishment of debt	3,115	2,741
Other Operating Income (Expense), Net	(509)	58
Income (loss) on variable interest entities	574	3,701
Total revenues	174,057	126,372
Expenses:
Losses and loss expenses (benefit)	(247,395)	135,011
Insurance intangible amortization	28,636	37,525
Operating expenses	36,434	28,124
Interest expense	48,073	31,572
Total expenses	(134,252)	232,232
Pre-tax income (loss)	308,309	(105,860)
Provision for income taxes	2,605	19,581
Net income (loss)	305,704	(125,441)
Net income (loss) attributable to common stockholders	305,704	(125,441)
Other comprehensive income (loss), after tax:
Net income (loss)	305,704	(125,441)
Unrealized gains (losses) on securities, net of income tax provision (benefit) of ($1,708) and $0	122,304	21,335
Gains (losses) on foreign currency translation, net of income tax provision of $0 and $0	32,056	12,593
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Unrealized Gain (Loss) Arising During Period, after Tax	1,114
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, after Tax and Reclassification Adjustment, Attributable to Parent		0
Changes to postretirement benefit, net of income tax of $0 and $0	(859)	2,287
Total other comprehensive income (loss), net of income tax	154,615	36,215
Total comprehensive income (loss)	460,319	(89,226)
Less: comprehensive (gain) loss attributable to the noncontrolling interest:
Total comprehensive income (loss) attributable to Ambac Financial Group, Inc.	$ 460,319	$ (89,226)
Earnings Per Share, Basic	$ 6.72	$ (2.77)
Earnings Per Share, Diluted	$ 6.70	$ (2.77)