Financial Guarantee Insurance Contracts - Summary of Rollforward of RMBS Subrogation, by Estimation Approach (Detail) - Successor [Member] - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Summary Of Rollforward Of Subrogation By Estimation Approach [Line Items]
Litigation Settlement, Amount			$ 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	1,892,974		1,907,035
Random Samples [Member]
Subrogation By Estimation Approach [Roll Forward]
Discounted RMBS subrogation (gross of reinsurance), beginning balance	1,907,035	$ 2,829,575	2,829,575
Changes recognized
Impact of sponsor actions	0	(995,000)
Other Changes Rmbs Subrogation	(14,061)	20,498
Discounted RMBS subrogation (gross of reinsurance), ending balance	$ 1,892,974	$ 1,855,073	$ 1,907,035