Consolidated Statements of Total Comprehensive Income - Successor [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Revenues:
Net premiums earned	$ 52,989	$ 53,218	$ 143,754	$ 147,420
Net investment income:
Securities available-for-sale and short-term	80,999	79,530	235,092	201,880
Other investments	6,178	11,387	18,804	20,616
Total net investment income	87,177	90,917	253,896	222,496
Other-than-temporary impairment losses:
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities	(25,664)	(15,906)	(48,581)	(82,856)
Portion of other-than-temporary impairment recognized in other comprehensive income	12,154	13,053	29,366	63,228
Net other-than-temporary impairments	(13,510)	(2,853)	(19,215)	(19,628)
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments	6,150	11,749	5,434	27,748
Change in fair value of credit derivatives:
Gain (Loss) on Sale of Derivatives	134	226	1,467	711
Unrealized gains (losses)	45	1,507	6,388	17,843
Net change in fair value of credit derivatives	179	1,733	7,855	18,554
Net gains (losses) on interest rate derivatives	3,984	(14,510)	36,538	(134,265)
Net realized gains (losses) on extinguishment of debt	0	24	4,920	4,845
Other Operating Income (Expense), Net	46	2,693	427	17,611
Income (loss) on variable interest entities	(4,049)	2,057	(1,567)	(16,119)
Total revenues	132,966	145,028	432,042	268,662
Expenses:
Losses and loss expenses (benefit)	209,806	(69,204)	410,917	(226,981)
Insurance intangible amortization	45,690	44,553	116,686	134,456
Operating expenses	33,791	21,466	92,822	77,470
Interest expense	29,145	31,493	88,951	92,632
Total expenses	318,432	28,308	709,376	77,577
Pre-tax income (loss)	(185,466)	116,720	(277,334)	191,085
Provision for income taxes	5,439	15,282	31,902	21,877
Net income (loss)	(190,905)	101,438	(309,236)	169,208
Less: net gain (loss) attributable to noncontrolling interest	0	(36)	0	(328)
Net income (loss) attributable to common shareholders	(190,905)	101,474	(309,236)	169,536
Other comprehensive income (loss), after tax:
Net income (loss)	(190,905)	101,438	(309,236)	169,208
Unrealized gains (losses) on securities, net of deferred income taxes of $0	(434)	24,719	33,550	132,680
Gains (losses) on foreign currency translation, net of deferred income taxes of $0	24,624	(13,323)	66,509	(86,256)
Changes to postretirement benefit, net of tax of $0	(338)	(254)	1,611	278
Total other comprehensive income (loss), net of tax	23,852	11,142	101,670	46,702
Total comprehensive income (loss)	(167,053)	112,580	(207,566)	215,910
Less: comprehensive (gain) loss attributable to the noncontrolling interest:
Net gain (loss)	0	36	0	328
Total comprehensive income (loss) attributable to Ambac Financial Group, Inc.	$ (167,053)	$ 112,616	$ (207,566)	$ 216,238
Earnings Per Share, Basic	$ (4.20)	$ 2.24	$ (6.82)	$ 3.75
Earnings Per Share, Diluted	$ (4.20)	$ 2.22	$ (6.82)	$ 3.74