Special Purpose Entities, Including Variable Interest Entities - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	2 Months Ended	6 Months Ended			2 Months Ended	1 Months Ended	3 Months Ended	4 Months Ended	6 Months Ended				2 Months Ended	1 Months Ended	3 Months Ended	4 Months Ended	6 Months Ended				6 Months Ended	12 Months Ended
	Jun. 30, 2013	Jun. 30, 2013	Apr. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Successor Ambac [Member]	Apr. 30, 2013 Predecessor Ambac [Member]	Jun. 30, 2012 Predecessor Ambac [Member]	Apr. 30, 2013 Predecessor Ambac [Member]	Jun. 30, 2012 Predecessor Ambac [Member]	Jun. 30, 2013 Asset-Backed Securities and Utility Obligations [Member]	Jun. 30, 2013 Sponsored Variable Interest Entities [Member] Transactions	Dec. 31, 2012 Sponsored Variable Interest Entities [Member]	Jun. 30, 2013 Financial Guarantee [Member] Successor Ambac [Member]	Apr. 30, 2013 Financial Guarantee [Member] Predecessor Ambac [Member]	Jun. 30, 2012 Financial Guarantee [Member] Predecessor Ambac [Member]	Apr. 30, 2013 Financial Guarantee [Member] Predecessor Ambac [Member]	Jun. 30, 2012 Financial Guarantee [Member] Predecessor Ambac [Member]	Jun. 30, 2013 Variable Interest Entity [Member]	Apr. 30, 2013 Variable Interest Entity [Member]	Dec. 31, 2012 Variable Interest Entity [Member]	Jun. 30, 2013 Consolidated Entities [Member] Entity	Dec. 31, 2012 Consolidated Entities [Member] Entity
Variable Interest Entities [Line Items]
Debt outstanding to third parties under secured borrowing transaction																		$ 5,759		$ 14,588
Securities fair value	235,850	235,850		201,329														235,850		201,329
Fair value of special purpose entities	13,884	13,884		14,557
Number of individual transactions with special purpose entities											15
Number of transactions outstanding with special purpose entities											3
Total principal amount of debt outstanding											464,495	466,938
Weighted average life										8 years 8 months 12 days
Average rating of assets held by sponsored special purpose entities		BBB+
Earned premiums for issuing the financial guarantee policies on the assets, MTNs and derivative contracts					20	10	110	40	255
Assets sold to special purpose entities					0	0	9,710	1,455	9,844
Claims on insurance policies issued to these entities		0
Earned fees for providing other services under its financial guarantee policies													2	1	11	3	22
Amount received under derivative contracts					1,222		3,886		3,747
Amount paid under derivative contracts						0		93
Number of consolidated Variable Interest Entities																					19	18
Consolidated VIE assets	16,263,319	16,263,319		17,841,863
Consolidated VIE liabilities	16,265,628	16,265,628		17,661,700
Intangible assets recorded at fair value			164,520																164,520
Weighted-average amortization period		16 years
Amortization expense for intangible assets	$ 2,508