Financial Guarantee Insurance Contracts - Summary of Balance of RMBS Subrogation Recoveries and Related Claim Liabilities, by Estimation Approach (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items]
Balance Of Rmbs Subrogation Recoveries Net Of Reinsurance	$ (1,856,565)		$ (1,878,740)
Successor [Member]
Schedule Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items]
Subrogation recoveries	1,884,456		1,907,035
Successor [Member] | Random Samples [Member]
Schedule Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items]
Gross loss reserve before subrogation recoveries	1,360,985		1,351,640
Subrogation recoveries	1,884,456		1,907,035
Gross loss reserve after subrogation recoveries	(523,471)		(555,395)
Random Samples [Member] | Successor [Member]
Schedule Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items]
Subrogation recoveries	1,884,456	$ 1,883,826	$ 1,907,035	$ 2,829,575
Impact Of Sponsor Actions In Residential Mortgage Backed Securities Subrogation	0	(995,000)
Other Changes Rmbs Subrogation	$ (22,579)	$ 49,251