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	3 Months Ended	5 Months Ended	3 Months Ended	5 Months Ended	3 Months Ended	5 Months Ended	3 Months Ended	4 Months Ended	9 Months Ended	3 Months Ended	4 Months Ended	9 Months Ended	3 Months Ended	4 Months Ended	9 Months Ended	3 Months Ended	4 Months Ended	9 Months Ended
	Sep. 30, 2013 Successor Ambac [Member]	Sep. 30, 2013 Successor Ambac [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, 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, 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, 2012 Predecessor Ambac [Member]	Apr. 30, 2013 Predecessor Ambac [Member]	Sep. 30, 2012 Predecessor Ambac [Member]	Sep. 30, 2012 Predecessor Ambac [Member] Reportable Geographical Components [Member] United States [Member]	Apr. 30, 2013 Predecessor Ambac [Member] Reportable Geographical Components [Member] United States [Member]	Sep. 30, 2012 Predecessor Ambac [Member] Reportable Geographical Components [Member] United States [Member]	Sep. 30, 2012 Predecessor Ambac [Member] Reportable Geographical Components [Member] United Kingdom [Member]	Apr. 30, 2013 Predecessor Ambac [Member] Reportable Geographical Components [Member] United Kingdom [Member]	Sep. 30, 2012 Predecessor Ambac [Member] Reportable Geographical Components [Member] United Kingdom [Member]	Sep. 30, 2012 Predecessor Ambac [Member] Reportable Geographical Components [Member] Other International [Member]	Apr. 30, 2013 Predecessor Ambac [Member] Reportable Geographical Components [Member] Other International [Member]	Sep. 30, 2012 Predecessor Ambac [Member] Reportable Geographical Components [Member] Other International [Member]
Segment Reporting Information [Line Items]
Gross Premiums Written	$ (34,380)	$ (68,461)	$ (25,030)	$ (49,523)	$ (2,789)	$ (4,706)	$ (6,561)	$ (14,232)	$ (55,310)	$ (14,125)	$ (175,777)	$ (40,748)	$ (16,102)	$ (165,408)	$ (1,060)	$ 10,673	$ 11,325	$ (13,502)	$ (8,696)	$ (21,694)
Net Premiums Earned	70,949	128,988	50,234	96,574	15,273	24,113	5,442	8,301	113,074	130,000	311,066	92,132	104,594	235,672	14,763	18,071	55,355	6,179	7,335	20,039
Net Change In Fair Value Of Credit Derivatives	$ 31,194	$ 82,414	$ 21,911	$ 36,860	$ 948	$ 3,061	$ 8,335	$ 42,493	$ 27,440	$ (60,384)	$ 12,803	$ 15,845	$ (31,134)	$ 7,577	$ 716	$ (5,861)	$ (3,721)	$ 10,879	$ (23,389)	$ 8,947