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	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Apr. 30, 2013
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Ceded Loss And Loss Expenses Paid Not Yet ecovered	$ (130)	$ (1,108)
Loss and loss expense reserves	6,003,474	5,968,712
Subrogation recoverable	(489,237)	(498,478)
Successor Ambac [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Loss Reserves Ceded To Reinsurers	105,641	122,357	123,425	138,155
Liability for Claims	$ 5,514,237	$ 5,470,234	$ 5,400,055	$ 5,572,672