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Financial Guarantee Insurance Contracts - Summary of Loss Reserve Roll-Forward, Net of Subrogation Recoverable and Reinsurance (Detail) - Successor [Member] - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Sep. 30, 2014
Mar. 31, 2016
Dec. 31, 2015
Mar. 31, 2015
Loss And Loss Adjustment Expense Reserves [Line Items]            
Ceded Loss And Loss Expenses Paid Not Yet Recovered       $ (162) $ (60) $ 4,789
Policyholder Benefits and Claims Incurred, Ceded $ (9,454)   $ (20,601)      
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]            
Beginning gross loss and loss expense reserves 2,858,813 $ 3,798,733        
Less reinsurance on loss and loss expense reserves 44,059 100,355        
Beginning balance of net loss and loss expense reserves 2,814,754 3,698,378        
Current year:            
ambc_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsCurrentYear 768 1        
Claim and loss expense payments, net of subrogation and reinsurance 0 0        
Total current year 768 1        
Prior years:            
Change in previously established loss and loss expense reserves, gross of RMBS subrogation and net of reinsurance (95,811) (132,639)        
Claim and loss expense (payments) recoveries, net of subrogation and reinsurance (916,206) 104,202        
Change in previously established RMBS subrogation recoveries, net of reinsurance (20,319) (44,195)        
Liability For Unpaid Claims And Claims Adjustment Expense Change In Loss Reserves Prior Year 800,076 (281,036)        
Net change in loss and loss expense reserves 800,844 (281,035)        
Liability for Unpaid Claims and Claims Adjustment Expense, Net 2,814,754 3,698,378   $ 3,615,598 $ 2,814,754 $ 3,417,343
Add reinsurance on loss and loss expense reserves 27,478 74,519        
Ending gross loss and loss expense reserves $ 3,643,076 $ 3,491,862