Segment Information - Schedule of Gross Premiums Written, Net Premiums Earned and Net Change in Fair Value of Credit Derivatives (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		5 Months Ended	9 Months Ended	3 Months Ended		5 Months Ended	9 Months Ended	3 Months Ended		5 Months Ended	9 Months Ended	3 Months Ended		5 Months Ended	9 Months Ended	4 Months Ended
	Sep. 30, 2014 Successor Ambac [Member]	Sep. 30, 2013 Successor Ambac [Member]	Sep. 30, 2013 Successor Ambac [Member]	Sep. 30, 2014 Successor Ambac [Member]	Sep. 30, 2014 Successor Ambac [Member] Reportable Geographical Components [Member] United States [Member]	Sep. 30, 2013 Successor Ambac [Member] Reportable Geographical Components [Member] United States [Member]	Sep. 30, 2013 Successor Ambac [Member] Reportable Geographical Components [Member] United States [Member]	Sep. 30, 2014 Successor Ambac [Member] Reportable Geographical Components [Member] United States [Member]	Sep. 30, 2014 Successor Ambac [Member] Reportable Geographical Components [Member] United Kingdom [Member]	Sep. 30, 2013 Successor Ambac [Member] Reportable Geographical Components [Member] United Kingdom [Member]	Sep. 30, 2013 Successor Ambac [Member] Reportable Geographical Components [Member] United Kingdom [Member]	Sep. 30, 2014 Successor Ambac [Member] Reportable Geographical Components [Member] United Kingdom [Member]	Sep. 30, 2014 Successor Ambac [Member] Reportable Geographical Components [Member] Other International [Member]	Sep. 30, 2013 Successor Ambac [Member] Reportable Geographical Components [Member] Other International [Member]	Sep. 30, 2013 Successor Ambac [Member] Reportable Geographical Components [Member] Other International [Member]	Sep. 30, 2014 Successor Ambac [Member] Reportable Geographical Components [Member] Other International [Member]	Apr. 30, 2013 Predecessor Ambac [Member]	Apr. 30, 2013 Predecessor Ambac [Member] Reportable Geographical Components [Member] United States [Member]	Apr. 30, 2013 Predecessor Ambac [Member] Reportable Geographical Components [Member] United Kingdom [Member]	Apr. 30, 2013 Predecessor Ambac [Member] Reportable Geographical Components [Member] Other International [Member]
Segment Reporting Information [Line Items]
Gross Premiums Written	$ (13,700)	$ (34,380)	$ (68,461)	$ (64,952)	$ (15,355)	$ (25,030)	$ (49,523)	$ (44,266)	$ 1,482	$ (2,789)	$ (4,706)	$ (1,681)	$ 173	$ (6,561)	$ (14,232)	$ (19,005)	$ (14,125)	$ (16,102)	$ 10,673	$ (8,696)
Net premiums earned	64,831	70,949	128,988	212,391	44,882	50,234	96,574	141,472	14,309	15,273	24,113	55,752	5,640	5,442	8,301	15,167	130,000	104,594	18,071	7,335
Net Change In Fair Value Of Credit Derivatives	$ 7,416	$ 31,194	$ 82,414	$ 13,579	$ 262	$ 21,911	$ 36,860	$ 6,283	$ 0	$ 948	$ 3,061	$ 0	$ 7,154	$ 8,335	$ 42,493	$ 7,296	$ (60,384)	$ (31,134)	$ (5,861)	$ (23,389)