Financial Guarantee Insurance Contracts - Summary of Rollforward of RMBS Subrogation, by Estimation Approach (Detail) - Successor [Member] - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Mar. 31, 2016	Sep. 30, 2017	Sep. 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		1,844,116
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		(62,919)	88,681
Discounted RMBS subrogation (gross of reinsurance), ending balance		$ 1,844,116	$ 1,923,256