Financial Guarantee Insurance Contracts - Summary of Balance of RMBS Subrogation Recoveries and Related Claim Liabilities, by Estimation Approach (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013 Successor Ambac [Member] Transactions	Jun. 30, 2013 Successor Ambac [Member] Adverse Samples [Member] Transactions	Jun. 30, 2013 Successor Ambac [Member] Random Samples [Member] Transactions	Dec. 31, 2012 Predecessor Ambac [Member] Transactions	Dec. 31, 2012 Predecessor Ambac [Member] Adverse Samples [Member] Transactions	Dec. 31, 2012 Predecessor Ambac [Member] Random Samples [Member] Transactions
Schedule Of Balance Of Rmbs Subrogation Recoveries And Related Claim Liabilities By Estimation Approach [Line Items]
Count	50	29	21	49	27	22
Gross loss reserve before subrogation recoveries	$ 3,408,648	$ 2,323,908	$ 1,084,740	$ 3,563,344	$ 2,331,878	$ 1,231,466
Subrogation recoveries	(2,394,933)	(1,436,328)	(958,605)	(2,523,225)	(1,442,817)	(1,080,408)
Gross loss reserve after subrogation recoveries	$ 1,013,715	$ 887,580	$ 126,135	$ 1,040,119	$ 889,061	$ 151,058