Financial Guarantee Insurance Contracts - Summary of Loss Reserve Roll-Forward, Net of Subrogation Recoverable and Reinsurance (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Prior years:
Add reinsurance on loss and loss expense reserves	$ 71,031		$ 71,031
Successor [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Ceded Loss And Loss Expenses Paid Not Yet Recovered	4,974	$ (760)			$ (517)
Policyholder Benefits and Claims Incurred, Ceded	(3,219)	(1,602)	(23,821)	$ (12,160)
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning gross loss and loss expense reserves			3,798,733	5,470,234
Less reinsurance on loss and loss expense reserves			100,355	122,357
Beginning balance of net loss and loss expense reserves			3,698,378	5,347,877
Current year:
ambc_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsCurrentYear			737	209
Claim and loss expense payments, net of subrogation and reinsurance			0	3
Total current year			737	206
Prior years:
Change in previously established loss and loss expense reserves, gross of RMBS subrogation and net of reinsurance			(262,962)	131,124
Claim and loss expense (payments) recoveries, net of subrogation and reinsurance			88,387	(73,347)
Change in previously established RMBS subrogation recoveries, net of reinsurance			(32,785)	(74,398)
Liability For Unpaid Claims And Claims Adjustment Expense Change In Loss Reserves Prior Year			(384,134)	130,073
Net change in loss and loss expense reserves			(383,397)	130,279
Liability for Unpaid Claims and Claims Adjustment Expense, Net	3,314,981	5,478,156	3,698,378	5,347,877	$ 3,698,378
Add reinsurance on loss and loss expense reserves	71,031	110,015	71,031	110,015
Ending gross loss and loss expense reserves	$ 3,386,012	$ 5,588,171	$ 3,386,012	$ 5,588,171