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	2 Months Ended				1 Months Ended	3 Months Ended	4 Months Ended	6 Months Ended	1 Months Ended	3 Months Ended	4 Months Ended	6 Months Ended	1 Months Ended	3 Months Ended	4 Months Ended	6 Months Ended	1 Months Ended	3 Months Ended	4 Months Ended	6 Months Ended
	Jun. 30, 2013 Successor Ambac [Member]	Jun. 30, 2013 Successor Ambac [Member] United States [Member]	Jun. 30, 2013 Successor Ambac [Member] United Kingdom [Member]	Jun. 30, 2013 Successor Ambac [Member] Other International [Member]	Apr. 30, 2013 Predecessor Ambac [Member]	Jun. 30, 2012 Predecessor Ambac [Member]	Apr. 30, 2013 Predecessor Ambac [Member]	Jun. 30, 2012 Predecessor Ambac [Member]	Apr. 30, 2013 Predecessor Ambac [Member] United States [Member]	Jun. 30, 2012 Predecessor Ambac [Member] United States [Member]	Apr. 30, 2013 Predecessor Ambac [Member] United States [Member]	Jun. 30, 2012 Predecessor Ambac [Member] United States [Member]	Apr. 30, 2013 Predecessor Ambac [Member] United Kingdom [Member]	Jun. 30, 2012 Predecessor Ambac [Member] United Kingdom [Member]	Apr. 30, 2013 Predecessor Ambac [Member] United Kingdom [Member]	Jun. 30, 2012 Predecessor Ambac [Member] United Kingdom [Member]	Apr. 30, 2013 Predecessor Ambac [Member] Other International [Member]	Jun. 30, 2012 Predecessor Ambac [Member] Other International [Member]	Apr. 30, 2013 Predecessor Ambac [Member] Other International [Member]	Jun. 30, 2012 Predecessor Ambac [Member] Other International [Member]
Segment Reporting Information [Line Items]
Gross Premiums Written	$ (34,081)	$ (24,493)	$ (1,917)	$ (7,671)	$ (10,595)	$ (27,873)	$ (14,125)	$ (120,467)	$ (7,386)	$ (31,936)	$ (16,102)	$ (124,661)	$ 2,167	$ 5,971	$ 10,673	$ 12,385	$ (5,376)	$ (1,908)	$ (8,696)	$ (8,191)
Net Premiums Earned	58,039	46,340	8,840	2,859	29,744	103,042	130,000	197,992	23,537	70,555	104,594	143,541	4,317	25,551	18,071	40,592	1,890	6,936	7,335	13,859
Net change in fair value of credit derivatives	$ 51,220	$ 14,948	$ 2,113	$ 34,159	$ (73,171)	$ (7,415)	$ (60,384)	$ (14,637)	$ (47,664)	$ (4,816)	$ (31,134)	$ (8,267)	$ (3,686)	$ (813)	$ (5,861)	$ (4,437)	$ (21,821)	$ (1,786)	$ (23,389)	$ (1,933)