Financial Guarantee Insurance Contracts - Summary of Loss Reserve Roll-Forward, Net of Subrogation Recoverable and Reinsurance (Detail) - USD ($) $ in Thousands	4 Months Ended	8 Months Ended	12 Months Ended
	Apr. 30, 2013	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Apr. 30, 2013
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Less reinsurance on loss and loss expense reserves			$ 100,355
Prior years:
Add reinsurance on loss and loss expense reserves			44,059	$ 100,355
Successor [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Ceded Loss And Loss Expenses Paid Not Yet Recovered					$ (60)	$ (517)	$ (1,108)
Policyholder Benefits and Claims Incurred, Ceded		$ (14,106)	(47,085)	(21,164)
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning gross loss and loss expense reserves		5,572,672	3,798,733	5,470,234
Less reinsurance on loss and loss expense reserves		138,155	100,355	122,357
Beginning balance of net loss and loss expense reserves		5,434,517	3,698,378	5,347,877
Current year:
ambc_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsCurrentYear		97,342	1,183	309
Claim and loss expense payments, net of subrogation and reinsurance		442	0	17
Establishment of RMBS subrogation recoveries, net of reinsurance		(315)	0	0
Total current year		96,585	1,183	292
Prior years:
Change in previously established loss and loss expense reserves, gross of RMBS subrogation and net of reinsurance		(514,728)	(491,088)	(269,606)
Claim and loss expense (payments) recoveries, net of subrogation and reinsurance		(59,184)	90,086	1,067,321
Change in previously established RMBS subrogation recoveries, net of reinsurance		272,319	(303,633)	(312,864)
Liability For Unpaid Claims And Claims Adjustment Expense Change In Loss Reserves Prior Year		(183,225)	(884,807)	(1,649,791)
Net change in loss and loss expense reserves		(86,640)	(883,624)	(1,649,499)
Consolidation Of Variable Interest Entities On Loss And Loss Adjustment Expense Reserves					0	0	0
Liability for Unpaid Claims and Claims Adjustment Expense, Net		5,434,517	3,698,378	5,347,877	$ 2,814,754	$ 3,698,378	$ 5,347,877	$ 5,434,517
Add reinsurance on loss and loss expense reserves	$ 138,155	122,357	44,059	100,355
Ending gross loss and loss expense reserves	5,572,672	5,470,234	$ 2,858,813	$ 3,798,733
Predecessor [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Ceded Loss And Loss Expenses Paid Not Yet Recovered								1,879
Policyholder Benefits and Claims Incurred, Ceded	3,889
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning gross loss and loss expense reserves	6,122,140	5,572,672
Less reinsurance on loss and loss expense reserves	147,409	138,155
Beginning balance of net loss and loss expense reserves	5,974,731	5,434,517
Current year:
ambc_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsCurrentYear	2,748
Claim and loss expense payments, net of subrogation and reinsurance	58
Establishment of RMBS subrogation recoveries, net of reinsurance	(159)
Total current year	2,531
Prior years:
Change in previously established loss and loss expense reserves, gross of RMBS subrogation and net of reinsurance	(52,642)
Claim and loss expense (payments) recoveries, net of subrogation and reinsurance	(20,902)
Change in previously established RMBS subrogation recoveries, net of reinsurance	(12,596)
Liability For Unpaid Claims And Claims Adjustment Expense Change In Loss Reserves Prior Year	(44,336)
Net change in loss and loss expense reserves	(41,805)
Consolidation Of Variable Interest Entities On Loss And Loss Adjustment Expense Reserves								(498,409)
Liability for Unpaid Claims and Claims Adjustment Expense, Net	5,974,731	$ 5,434,517						$ 5,434,517
Add reinsurance on loss and loss expense reserves	138,155
Ending gross loss and loss expense reserves	$ 5,572,672