Financial Guarantee Insurance Contracts - Summary of Information Related to Policies Currently Included in Ambac's Loss Reserves or Subrogation Recoverable (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Loss Reserves Ceded To Reinsurers	$ 74,519	$ 100,355
Ceded Loss And Loss Expenses Paid Not Yet Recovered	4,789	139	(517)
Successor [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Loss Reserves Ceded To Reinsurers	74,519	100,355	111,303	122,357
Loss and loss expense reserves	4,475,991	4,752,007
Subrogation recoverable	(984,129)	(953,274)
Liability for Claims	$ 3,491,862	$ 3,798,733	$ 5,313,933	$ 5,470,234