Special Purpose Entities, Including Variable Interest Entities - Additional Information (Detail) (USD $)	3 Months Ended		3 Months Ended	9 Months Ended	4 Months Ended	9 Months Ended				3 Months Ended	5 Months Ended		1 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013 Successor [Member]	Sep. 30, 2014 Successor [Member]	Apr. 30, 2013 Predecessor Ambac [Member]	Sep. 30, 2014 Asset-Backed Securities and Utility Obligations [Member]	Sep. 30, 2014 Sponsored Variable Interest Entities [Member] Transactions	Dec. 31, 2013 Sponsored Variable Interest Entities [Member]	Sep. 30, 2014 Variable Interest Entity, Primary Beneficiary [Member]	Sep. 30, 2013 Variable Interest Entities [Member] Successor [Member]	Sep. 30, 2013 Variable Interest Entities [Member] Successor [Member]	Dec. 31, 2013 Variable Interest Entities [Member] Successor [Member]	Apr. 30, 2013 Variable Interest Entities [Member] Predecessor Ambac [Member]	Sep. 30, 2014 Consolidated Entities [Member] Entity	Dec. 31, 2013 Consolidated Entities [Member] Entity
Variable Interest Entities [Line Items]
Variable Interest Entity, Initial Consolidation, Gain (Loss)													$ 385,291,000
Secured Debt									0
Securities fair value	0	240,150,000
Fair value of special purpose entities	12,401,000	13,384,000
Number of individual transactions with special purpose entities							15
Number of transactions outstanding with special purpose entities							3
Total principal amount of debt outstanding							461,355,000	461,355,000
Weighted average life						7 years 9 months 12 days
Average rating of assets held by sponsored special purpose entities						BBB
Claims on insurance policies issued to these entities			2,747,000	988,000	1,455,000
Number of consolidated Variable Interest Entities														15	18
Consolidated VIE assets	15,169,675,000	15,988,697,000
Consolidated VIE liabilities	15,120,775,000	15,872,770,000
Fair Value Intangible Assets Initially Recorded Upon Consolidation Of Variable Interest Entity													164,520,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life													16 years 0 months 0 days
Amortization Of Variable Interest Entity Intangible Assets										2,507,000	5,015,000
Asset Impairment Charges												76,140
Variable Interest Entity Deconsolidation Gain Loss	$ 0