Fair Value Measurements - Summary of Gains and Losses (Realized and Unrealized) Relating to Level 3 Assets and Liabilities Included in Earnings (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	2 Months Ended	1 Months Ended	3 Months Ended	4 Months Ended	6 Months Ended
	Jun. 30, 2013 Successor Ambac [Member] Variable Interest Entity [Member]	Apr. 30, 2013 Predecessor Ambac [Member] Variable Interest Entity [Member]	Jun. 30, 2012 Predecessor Ambac [Member] Variable Interest Entity [Member]	Apr. 30, 2013 Predecessor Ambac [Member] Variable Interest Entity [Member]	Jun. 30, 2012 Predecessor Ambac [Member] Variable Interest Entity [Member]	Jun. 30, 2013 Realized gains or (losses) and other settlements on credit derivative contracts [Member] Successor Ambac [Member]	Apr. 30, 2013 Realized gains or (losses) and other settlements on credit derivative contracts [Member] Predecessor Ambac [Member]	Jun. 30, 2012 Realized gains or (losses) and other settlements on credit derivative contracts [Member] Predecessor Ambac [Member]	Apr. 30, 2013 Realized gains or (losses) and other settlements on credit derivative contracts [Member] Predecessor Ambac [Member]	Jun. 30, 2012 Realized gains or (losses) and other settlements on credit derivative contracts [Member] Predecessor Ambac [Member]	Jun. 30, 2013 Unrealized gains or (losses) on credit derivative contracts [Member] Successor Ambac [Member]	Apr. 30, 2013 Unrealized gains or (losses) on credit derivative contracts [Member] Predecessor Ambac [Member]	Jun. 30, 2012 Unrealized gains or (losses) on credit derivative contracts [Member] Predecessor Ambac [Member]	Apr. 30, 2013 Unrealized gains or (losses) on credit derivative contracts [Member] Predecessor Ambac [Member]	Jun. 30, 2012 Unrealized gains or (losses) on credit derivative contracts [Member] Predecessor Ambac [Member]	Jun. 30, 2013 Interest Rate Swaps [Member] Successor Ambac [Member]	Apr. 30, 2013 Interest Rate Swaps [Member] Predecessor Ambac [Member]	Jun. 30, 2012 Interest Rate Swaps [Member] Predecessor Ambac [Member]	Apr. 30, 2013 Interest Rate Swaps [Member] Predecessor Ambac [Member]	Jun. 30, 2012 Interest Rate Swaps [Member] Predecessor Ambac [Member]	Jun. 30, 2013 Other income [Member] Successor Ambac [Member]	Apr. 30, 2013 Other income [Member] Predecessor Ambac [Member]	Jun. 30, 2012 Other income [Member] Predecessor Ambac [Member]	Apr. 30, 2013 Other income [Member] Predecessor Ambac [Member]	Jun. 30, 2012 Other income [Member] Predecessor Ambac [Member]	Jun. 30, 2013 Net investment income [Member] Successor Ambac [Member]	Apr. 30, 2013 Net investment income [Member] Predecessor Ambac [Member]	Jun. 30, 2012 Net investment income [Member] Predecessor Ambac [Member]	Apr. 30, 2013 Net investment income [Member] Predecessor Ambac [Member]	Jun. 30, 2012 Net investment income [Member] Predecessor Ambac [Member]
Total gains or losses included in earnings for the period																										$ 395	$ (10)	$ 88	$ (33)	$ 40
Total gains or losses included in earnings for the period	(791,292)	575,899	173,145	1,146,256	120,431	6,074	935	3,072	3,444	6,326	45,146	(74,106)	(10,489)	(63,828)	(20,964)	18,907	(12,213)	(112,904)	(28,162)	(45,035)	(177)	(169)	38,799	(496)	99,723
Changes in unrealized gains or losses relating to the assets and liabilities still held at the reporting date	$ (791,292)	$ 575,899	$ 173,145	$ 1,146,256	$ 120,912						$ 13,618	$ (74,107)	$ (10,613)	$ (63,840)	$ (26,647)	$ 18,907	$ (12,213)	$ (107,861)	$ (28,162)	$ (46,263)	$ (177)	$ (169)	$ (231)	$ (496)	$ (987)