Financial Guarantee Insurance Contracts - Summary of Information Related to Policies Currently Included in Ambac's Loss Reserves or Subrogation Recoverable (Phantom) (Detail) - Successor [Member] - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Loss Reserves Ceded To Reinsurers	$ 47,034	$ 30,767	$ 30,108	$ 44,059
Loss and loss expense reserves	4,582,153	4,380,769
Subrogation recoverable	(658,875)	(684,731)
Liability for Claims	3,923,278	3,696,038	3,650,781	$ 2,858,813
Ceded Loss And Loss Expenses Paid Not Yet Recovered	$ (568)	$ (349)	$ (1,404)