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	Dec. 31, 2014	Dec. 31, 2013	Apr. 30, 2013
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Loss Reserves Ceded To Reinsurers	$ 100,355	$ 122,357
Ceded Loss And Loss Expenses Paid Not Yet Recovered	(517)	(1,108)
Successor [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Loss Reserves Ceded To Reinsurers	100,355	122,357	138,155
Loss and loss expense reserves	4,752,007	5,968,712	6,106,345
Subrogation recoverable	(953,274)	(498,478)	(533,673)
Liability for Claims	$ 3,798,733	$ 5,470,234	$ 5,572,672