Schedule II - Condensed Financial Information of Registrant (Parent Company Only) - Condensed Statement of Total Comprehensive Income (Detail) - Successor [Member] - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues:
Other income									$ 17,445	$ 7,150	$ 12,498
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net									(21,819)	(25,659)	(25,794)
Net realized investment gains									(39,284)	(53,476)	(58,777)
Total revenues before expenses and reorganization items									506,149	644,658	328,670
Expenses:
Reorganization items									0	0	211
Pre-tax income	$ (86,059)	$ 116,720	$ 61,511	$ 12,854	$ 395,576	$ (388,193)	$ 286,095	$ 216,580	105,026	510,058	493,253
Income tax expense (benefit)									(30,709)	(17,364)	(9,557)
Net income (loss)									74,317	492,694	483,696
Other comprehensive income, after tax:
Net income (loss)									74,317	492,694	483,696
Unrealized gains (losses) on securities, net of deferred income taxes of $0									67,900	(159,730)	252,603
Gains (losses) on foreign currency translation, net of deferred income taxes of $0									(122,128)	(45,025)	(43,599)
Total other comprehensive income (loss), net of tax									(54,205)	(205,442)	208,188
Total comprehensive income attributable to Ambac Financial Group, Inc.									20,638	288,335	692,693
Ambac Financial Group, Inc Parent Company Only [Member]
Revenues:
Investment income									13,493	9,826	25,147
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net									(289)	(155)	0
Net realized investment gains									7	27	46
Total revenues before expenses and reorganization items									13,197	9,644	25,101
Expenses:
Operating expenses									11,486	8,922	6,458
Total expenses									11,486	8,922	6,458
Income (loss) before income taxes, reorganization costs and equity in undistributed net loss of subsidiaries									1,711	722	18,643
Reorganization items									0	0	211
Pre-tax income									1,711	722	18,432
Income tax expense (benefit)									28,739	70,811	(221)
Income before equity in undistributed net income of subsidiaries									(30,450)	(71,533)	(18,211)
Equity in undistributed net income (loss) of subsidiaries									44,393	421,870	465,860
Net income (loss)									74,843	493,403	484,071
Other comprehensive income, after tax:
Net income (loss)									74,843	493,403	484,071
Unrealized gains (losses) on securities, net of deferred income taxes of $0									67,900	(159,730)	252,603
Gains (losses) on foreign currency translation, net of deferred income taxes of $0									(122,128)	(44,651)	(43,165)
Changes to postretirement benefit, net of tax									23	(687)	(816)
Total other comprehensive income (loss), net of tax									(54,205)	(205,068)	208,622
Total comprehensive income attributable to Ambac Financial Group, Inc.									$ 20,638	$ 288,335	$ 692,693