Fresh Start Financial Statement Reporting - Schedule of Impact of Fresh Start Adjustments (Detail) (Predecessor Ambac [Member], USD $) In Thousands, unless otherwise specified	Apr. 30, 2013	Dec. 31, 2012
Fresh-Start Adjustment [Line Items]
Deferred acquisition costs	$ (184,953)	$ (199,160)
Insurance intangible asset	1,658,972
Goodwill	514,511
Obligations under investment agreements	(1,505)
Long-term debt and accrued interest payable	(767,924)
Other liabilities	(1,837)
Asset/liability fair value adjustments impacting Reorganization items	1,228,251
Adjustment to deferred tax provision
Gain on fresh start adjustments	1,228,251
Non Variable Interest Entities [Member]
Fresh-Start Adjustment [Line Items]
Loans (non-VIE)	(1,575)
Variable Interest Entity [Member]
Fresh-Start Adjustment [Line Items]
VIE loans and long-term debt	$ 12,562