Derivative Instruments - Summarize Information by Major Category of CDS Contracts (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014 Transactions	Dec. 31, 2013 Transactions
Summary of information by major category of CDS contracts
Gross principal notional outstanding	$ 1,958,926	$ 2,776,103
Successor Ambac [Member]
Summary of information by major category of CDS contracts
Number of CDS transactions	17	20
Remaining expected weighted-average life of obligations (in years)	3 years 8 months 12 days	3 years 7 months 6 days
Gross principal notional outstanding	1,958,926	2,776,103
Successor Ambac [Member] | Credit Derivatives [Member]
Summary of information by major category of CDS contracts
Net derivative liabilities at fair value	82,830	94,322
CLO [Member] | Successor Ambac [Member]
Summary of information by major category of CDS contracts
Number of CDS transactions	6	7
Remaining expected weighted-average life of obligations (in years)	1 year 9 months 18 days	2 years 1 month 15 days
Gross principal notional outstanding	669,251	1,337,737
CLO [Member] | Successor Ambac [Member] | Credit Derivatives [Member]
Summary of information by major category of CDS contracts
Net derivative liabilities at fair value	2,726	7,993
Other [Member] | Successor Ambac [Member]
Summary of information by major category of CDS contracts
Number of CDS transactions	11	13
Remaining expected weighted-average life of obligations (in years)	4 years 8 months 12 days	5 years 0 months 15 days
Gross principal notional outstanding	1,289,675	1,438,366
Other [Member] | Successor Ambac [Member] | Credit Derivatives [Member]
Summary of information by major category of CDS contracts
Net derivative liabilities at fair value	$ 80,104	$ 86,329