Financial Guarantee Insurance Contracts - Summary of Rollforward of RMBS Subrogation, by Estimation Approach (Detail) (USD $) In Thousands, unless otherwise specified	2 Months Ended	4 Months Ended	2 Months Ended	4 Months Ended	2 Months Ended	4 Months Ended
	Jun. 30, 2013 Successor Ambac [Member] Transactions	Apr. 30, 2013 Predecessor Ambac [Member] Transactions	Jun. 30, 2013 Random Samples [Member] Successor Ambac [Member] Transactions	Apr. 30, 2013 Random Samples [Member] Predecessor Ambac [Member] Transactions	Jun. 30, 2013 Adverse Samples [Member] Successor Ambac [Member] Transactions	Apr. 30, 2013 Adverse Samples [Member] Predecessor Ambac [Member] Transactions
Summary Of Rollforward Of Subrogation By Estimation Approach [Line Items]
Discounted RMBS subrogation (gross of reinsurance), beginning balance	$ 2,482,918	$ 2,523,225	$ 1,004,252	$ 1,080,408	$ 1,478,666	$ 1,442,817
Changes recognized
Additional transactions reviewed
Additional adverse sample loans reviewed
Impact of sponsor actions	(2,489)	(54,195)	(2,489)	(54,195)
All other changes	(85,496)	13,888	(43,158)	(21,961)	(42,338)	35,849
Discounted RMBS subrogation (gross of reinsurance), ending balance	$ 2,394,933	$ 2,482,918	$ 958,605	$ 1,004,252	$ 1,436,328	$ 1,478,666
Discounted RMBS subrogation (gross of reinsurance), beginning balance		49	20	22	29	27
Changes recognized: Additional transactions reviewed
Additional adverse sample loans reviewed
Impact of sponsor actions			1
All other changes				(2)		2
Discounted RMBS subrogation (gross of reinsurance), ending balance	50		21	20	29	29