Financial Guarantee Insurance Contracts - Summary of Rollforward of RMBS Subrogation, by Estimation Approach (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		4 Months Ended	3 Months Ended	5 Months Ended	12 Months Ended	3 Months Ended	4 Months Ended	3 Months Ended	5 Months Ended	12 Months Ended	3 Months Ended	4 Months Ended
	Mar. 31, 2014 Successor Ambac [Member] Transactions	Mar. 31, 2013 Predecessor Ambac [Member]	Apr. 30, 2013 Predecessor Ambac [Member]	Mar. 31, 2014 Random Samples [Member] Successor Ambac [Member] Transactions	Sep. 30, 2013 Random Samples [Member] Successor Ambac [Member] Transactions	Dec. 31, 2013 Random Samples [Member] Successor Ambac [Member] Transactions	Mar. 31, 2013 Random Samples [Member] Predecessor Ambac [Member] Transactions	Apr. 30, 2013 Random Samples [Member] Predecessor Ambac [Member] Transactions	Mar. 31, 2014 Adverse Samples [Member] Successor Ambac [Member] Transactions	Sep. 30, 2013 Adverse Samples [Member] Successor Ambac [Member] Transactions	Dec. 31, 2013 Adverse Samples [Member] Successor Ambac [Member] Transactions	Mar. 31, 2013 Adverse Samples [Member] Predecessor Ambac [Member] Transactions	Apr. 30, 2013 Adverse Samples [Member] Predecessor Ambac [Member] Transactions
Subrogation By Estimation Approach [Roll Forward]
Discounted RMBS subrogation (gross of reinsurance), beginning balance	$ 2,206,598	$ 2,523,225	$ 2,523,225	$ 953,825			$ 1,080,408	$ 1,080,408	$ 1,252,773			$ 1,442,817	$ 1,442,817
Discounted RMBS subrogation (gross of reinsurance), beginning balance (transactions)	48			21			22	22	27			27	27
Changes recognized
Additional transactions reviewed
Additional adverse sample loans reviewed
Impact of sponsor actions	0	(54,195)		0			(54,195)
Impact of sponsor actions (transactions)							(2)
All other changes	17,697	18,339		51,789			(22,570)		(34,092)			40,909
All other changes (transactions)												2
Discounted RMBS subrogation (gross of reinsurance), ending balance	$ 2,224,295	$ 2,487,369		$ 1,005,614		$ 953,825	$ 1,003,643		$ 1,218,681		$ 1,252,773	$ 1,483,726
Discounted RMBS subrogation (gross of reinsurance), ending balance (transactions)	48			21		21	20		27		27	29
Additional Adverse Sample Loans Reviewed Number Of Transactions
Impact Of Sponsor Actions