Investments - Summary of Roll-Forward of Ambac's Cumulative Credit Losses on Debt Securities for Which Portion of Other-than-Temporary Impairment was Recognized in Other Comprehensive Income (Detail) - Successor [Member] - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Balance at beginning	$ 47,505	$ 17,800	$ 31,176	$ 14,062
Additions for credit impairments recognized on:
Securities not previously impaired	1,544	1,456
Securities previously impaired	14,785	2,282
Reductions for credit impairments previously recognized on:
Balance at end	$ 47,505	$ 17,800	$ 31,176	$ 14,062