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	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Loss Reserves Ceded To Reinsurers	$ 30,767	$ 44,059
Successor [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Loss Reserves Ceded To Reinsurers	30,767	44,059	$ 100,355	$ 122,357
Loss and loss expense reserves	4,380,769	4,088,106
Subrogation recoverable	(684,731)	(1,229,293)
Liability for Claims	3,696,038	2,858,813	3,798,733	$ 5,470,234
Ceded Loss And Loss Expenses Paid Not Yet Recovered	$ (349)	$ (60)	$ (517)