Investments - Summary of Net Investment Income (Detail) (USD $) In Thousands, unless otherwise specified	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]
Investment [Line Items]
Fixed income securities	$ 30,431	$ 31,766	$ 94,467	$ 118,097	$ 207,119
Short-term investments	162	82	444	677	758
Loans	84	38	204	146	420
Investment expense	(1,096)	(387)	(1,279)	(1,809)	(2,344)
Securities available-for-sale and short-term	29,581	31,499	93,836	117,111	205,953
Other investments	(3,015)	912		369
Total net investment income	$ 26,566	$ 32,411	$ 93,836	$ 117,480	$ 205,953