Financial Guarantee Insurance Contracts - Summary of Rollforward of RMBS Subrogation, by Estimation Approach (Detail) (USD $) In Thousands, unless otherwise specified	2 Months Ended	6 Months Ended	4 Months Ended	2 Months Ended	6 Months Ended	4 Months Ended	2 Months Ended	6 Months Ended	4 Months Ended
	Jun. 30, 2013 Successor Ambac [Member]	Jun. 30, 2014 Successor Ambac [Member]	Apr. 30, 2013 Predecessor Ambac [Member]	Jun. 30, 2013 Random Samples [Member] Successor Ambac [Member]	Jun. 30, 2014 Random Samples [Member] Successor Ambac [Member]	Apr. 30, 2013 Random Samples [Member] Predecessor Ambac [Member]	Jun. 30, 2013 Adverse Samples [Member] Successor Ambac [Member]	Jun. 30, 2014 Adverse Samples [Member] Successor Ambac [Member]	Apr. 30, 2013 Adverse Samples [Member] Predecessor Ambac [Member]
Subrogation By Estimation Approach [Roll Forward]
Discounted RMBS subrogation (gross of reinsurance), beginning balance	$ 2,482,918	$ 2,206,598	$ 2,523,225	$ 1,004,252	$ 953,825	$ 1,080,408	$ 1,478,666	$ 1,252,773	$ 1,442,817
Changes recognized
Additional Transactions Reviewed Changes in RMBS Subrogation		24,510			24,510
Changes in Estimation Approach In Rmbs Subrogation	0	123,236	0	0	1,341,917	0	0	(1,218,681)	0
Impact of sponsor actions	(2,489)	(90,000)	(54,195)	(2,489)	(90,000)	(54,195)	0	0	0
All other changes	(85,496)	20,080	13,888	(43,158)	54,172	(21,961)	(42,338)	(34,092)	35,849
Discounted RMBS subrogation (gross of reinsurance), ending balance	$ 2,394,933	$ 2,284,424	$ 2,482,918	$ 958,605	$ 2,284,424	$ 1,004,252	$ 1,436,328	$ 0	$ 1,478,666