Fair Value Measurements - Summary of Information about Described Model Inputs Used to Determine Fair Value of Each Class of Credit Derivatives (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Notional outstanding	$ 5,207,364	$ 11,281,777
Successor Ambac [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Notional outstanding	5,207,364
Successor Ambac [Member] | CLO [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Notional outstanding	1,609,378
Weighted average reference obligation price	$ 97.9
Weighted average life (WAL) in years	2 years 3 months 18 days
Weighted average credit rating	AA
Weighted average relative change ratio	35.40%
CVA percentage	16.30%
Fair value of derivative liabilities	(10,201)
Successor Ambac [Member] | Other [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Notional outstanding	2,495,813
Weighted average reference obligation price	$ 88.3
Weighted average life (WAL) in years	4 years 7 months 6 days
Weighted average credit rating	BBB+
Weighted average relative change ratio	38.40%
CVA percentage	33.00%
Fair value of derivative liabilities	(113,713)
Predecessor Ambac [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Notional outstanding		11,281,777
Predecessor Ambac [Member] | CLO [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Notional outstanding		6,155,767
Weighted average reference obligation price		$ 96.5
Weighted average life (WAL) in years		2 years 2 months 12 days
Weighted average credit rating		AA-
Weighted average relative change ratio		34.40%
CVA percentage		55.00%
Fair value of derivative liabilities		(34,645)
Predecessor Ambac [Member] | Other [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Notional outstanding		3,701,387
Weighted average reference obligation price		$ 86.9
Weighted average life (WAL) in years		4 years 2 months 12 days
Weighted average credit rating		A
Weighted average relative change ratio		38.20%
CVA percentage		55.00%
Fair value of derivative liabilities		$ (116,086)