Financial Guarantee Insurance Contracts - Summary of Balance of RMBS Subrogation Recoveries and Related Claim Liabilities, by Estimation Approach (Detail) (Successor Ambac [Member], USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Apr. 30, 2013
Schedule Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items]
Gross loss reserve before subrogation recoveries	$ 2,670,550	$ 3,163,772
Subrogation recoveries	(2,214,430)	(2,206,598)	(2,361,856)	(2,482,918)
Gross loss reserve after subrogation recoveries	456,120	957,174
Adverse Samples [Member]
Schedule Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items]
Gross loss reserve before subrogation recoveries		2,084,911
Subrogation recoveries		(1,252,773)
Gross loss reserve after subrogation recoveries		832,138
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	2,670,550	1,078,861
Subrogation recoveries	(2,214,430)	(953,825)
Gross loss reserve after subrogation recoveries	$ 456,120	$ 125,036