Financial Guarantee Insurance Contracts - Summary of Rollforward of RMBS Subrogation, by Estimation Approach (Detail) - Successor [Member] - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Subrogation By Estimation Approach [Roll Forward]
Discounted RMBS subrogation (gross of reinsurance), beginning balance	$ 1,834,387
Changes recognized
Discounted RMBS subrogation (gross of reinsurance), ending balance	1,816,385
Random Samples [Member]
Subrogation By Estimation Approach [Roll Forward]
Discounted RMBS subrogation (gross of reinsurance), beginning balance	1,834,387	$ 1,907,035
Changes recognized
Other Changes Rmbs Subrogation	(18,002)	(22,579)
Discounted RMBS subrogation (gross of reinsurance), ending balance	$ 1,816,385	$ 1,884,456