Financial Guarantee Insurance Contracts - Summary of Rollforward of RMBS Subrogation, by Estimation Approach (Detail) - Successor [Member] - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Mar. 31, 2016	Jun. 30, 2017	Jun. 30, 2016
Summary Of Rollforward Of Subrogation By Estimation Approach [Line Items]
Litigation Settlement, Amount (Deprecated 2017-01-31)	$ 995,000
Subrogation By Estimation Approach [Roll Forward]
Discounted RMBS subrogation (gross of reinsurance), beginning balance		$ 1,907,035
Changes recognized
Discounted RMBS subrogation (gross of reinsurance), ending balance		1,884,456
Random Samples [Member]
Subrogation By Estimation Approach [Roll Forward]
Discounted RMBS subrogation (gross of reinsurance), beginning balance	$ 2,829,575	1,907,035	$ 2,829,575
Changes recognized
Impact of sponsor actions		0	(995,000)
Other Changes Rmbs Subrogation		(22,579)	49,251
Discounted RMBS subrogation (gross of reinsurance), ending balance		$ 1,884,456	$ 1,883,826