Derivative Instruments - Summarize Information by Major Category of CDS Contracts (Detail) (USD $) In Thousands, unless otherwise specified			12 Months Ended		6 Months Ended		12 Months Ended		6 Months Ended		12 Months Ended		6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Dec. 31, 2012 Predecessor Ambac [Member] Transactions	Dec. 31, 2012 Predecessor Ambac [Member] Credit Derivatives [Member]	Jun. 30, 2013 Successor Ambac [Member] Transactions	Jun. 30, 2013 Successor Ambac [Member] Credit Derivatives [Member]	Dec. 31, 2012 CLO [Member] Predecessor Ambac [Member] Transactions	Dec. 31, 2012 CLO [Member] Predecessor Ambac [Member] Credit Derivatives [Member]	Jun. 30, 2013 CLO [Member] Successor Ambac [Member] Transactions	Jun. 30, 2013 CLO [Member] Successor Ambac [Member] Credit Derivatives [Member]	Dec. 31, 2012 Other [Member] Predecessor Ambac [Member] Transactions	Dec. 31, 2012 Other [Member] Predecessor Ambac [Member] Credit Derivatives [Member]	Jun. 30, 2013 Other [Member] Successor Ambac [Member] Transactions	Jun. 30, 2013 Other [Member] Successor Ambac [Member] Credit Derivatives [Member]
Summary of information by major category of CDS contracts
Number of CDS transactions			51		29		30		9		21		20
Remaining expected weighted-average life of obligations (in years)			3 years 7 months 6 days		4 years 3 months 18 days		2 years 2 months 12 days		2 years 6 months		5 years 2 months 12 days		5 years 1 month 6 days
Gross principal notional outstanding	$ 5,861,060	$ 11,281,777	$ 11,281,777		$ 5,861,060		$ 6,155,767		$ 1,750,217		$ 5,126,010		$ 4,110,843
Net derivative liabilities at fair value				$ (213,585)		$ (232,267)		$ (34,645)		$ (11,996)		$ (178,940)		$ (220,271)