Segment Information - Summary of Financial Information by Reportable Segment (Detail) (USD $) In Thousands, unless otherwise specified	2 Months Ended	1 Months Ended	3 Months Ended	4 Months Ended	6 Months Ended	2 Months Ended	1 Months Ended	3 Months Ended	4 Months Ended	6 Months Ended	2 Months Ended	1 Months Ended	3 Months Ended	4 Months Ended	6 Months Ended	2 Months Ended	1 Months Ended	3 Months Ended	4 Months Ended	6 Months Ended	2 Months Ended	1 Months Ended	3 Months Ended	4 Months Ended	6 Months Ended
	Jun. 30, 2013 Successor Ambac [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]	Jun. 30, 2013 Financial Guarantee [Member] Successor Ambac [Member]	Apr. 30, 2013 Financial Guarantee [Member] Predecessor Ambac [Member]	Jun. 30, 2012 Financial Guarantee [Member] Predecessor Ambac [Member]	Apr. 30, 2013 Financial Guarantee [Member] Predecessor Ambac [Member]	Jun. 30, 2012 Financial Guarantee [Member] Predecessor Ambac [Member]	Jun. 30, 2013 Financial Services [Member] Successor Ambac [Member]	Apr. 30, 2013 Financial Services [Member] Predecessor Ambac [Member]	Jun. 30, 2012 Financial Services [Member] Predecessor Ambac [Member]	Apr. 30, 2013 Financial Services [Member] Predecessor Ambac [Member]	Jun. 30, 2012 Financial Services [Member] Predecessor Ambac [Member]	Jun. 30, 2013 Corporate and Other [Member] Successor Ambac [Member]	Apr. 30, 2013 Corporate and Other [Member] Predecessor Ambac [Member]	Jun. 30, 2012 Corporate and Other [Member] Predecessor Ambac [Member]	Apr. 30, 2013 Corporate and Other [Member] Predecessor Ambac [Member]	Jun. 30, 2012 Corporate and Other [Member] Predecessor Ambac [Member]	Jun. 30, 2013 Inter-Segment Eliminations [Member] Successor Ambac [Member]	Apr. 30, 2013 Inter-Segment Eliminations [Member] Predecessor Ambac [Member]	Jun. 30, 2012 Inter-Segment Eliminations [Member] Predecessor Ambac [Member]	Apr. 30, 2013 Inter-Segment Eliminations [Member] Predecessor Ambac [Member]	Jun. 30, 2012 Inter-Segment Eliminations [Member] Predecessor Ambac [Member]
Revenues:
Unaffiliated customers	$ 242,785	$ 349,701	$ (5,961)	$ 641,128	$ 318,175	$ 160,275	$ 382,957	$ 87,665	$ 633,750	$ 357,492	$ 82,490	$ (33,266)	$ (93,682)	$ 7,339	$ (39,430)	$ 20	$ 10	$ 56	$ 39	$ 113
Inter-segment						399	214	1,397	940	2,896	(374)	(198)	(1,346)	(882)	(2,789)	5,425	197,055		197,055	645	(5,450)	(197,071)	(51)	(197,113)	(752)
Total revenues before expenses and reorganization items	242,785	349,701	(5,961)	641,128	318,175	160,674	383,171	89,062	634,690	360,388	82,116	(33,464)	(95,028)	6,457	(42,219)	5,445	197,065	56	197,094	758	(5,450)	(197,071)	(51)	(197,113)	(752)
Pre-tax income (loss) from continuing operations:
Unaffiliated customers	205,795	3,065,124	(813,561)	3,348,033	(559,939)	124,890	1,583,465	(717,187)	1,830,165	(510,900)	81,692	(35,614)	(96,257)	3,233	(44,587)	(787)	1,517,273	(117)	1,514,635	(4,452)
Inter-segment						(5,497)	(197,115)	(712)	(197,187)	315	(523)	(252)	(429)	(1,101)	(1,784)	6,020	197,367	1,141	198,288	1,469
Pre-tax income (loss) from continuing operations	205,795	3,065,124	(813,561)	3,348,033	(559,939)	119,393	1,386,350	(717,899)	1,632,978	(510,585)	81,169	(35,866)	(96,686)	2,132	(46,371)	5,233	1,714,640	1,024	1,712,923	(2,983)
Total assets	27,475,367	28,853,435	26,611,791	28,853,435	26,611,791	26,934,044	28,287,321	25,771,887	28,287,321	25,771,887	486,346	536,711	800,677	536,711	800,677	54,977	29,403	39,227	29,403	39,227
Net investment income	26,566	32,411	93,836	117,480	205,953	26,385	32,040	89,953	115,869	195,214	158	361	3,826	1,572	10,625	23	10	57	39	114
Insurance intangible amortization	24,952					24,952
Interest expense	21,144	7,860	31,855	31,025	65,694	20,776	7,542	30,205	29,718	62,254	368	318	1,650	1,307	3,440
Reorganization items	$ 424	$ (2,747,239)	$ 767	$ (2,745,180)	$ 3,228		$ (1,231,550)		$ (1,231,550)			$ 1,505		$ 1,505		$ 424	$ (1,517,194)	$ 767	$ (1,515,135)	$ 3,228