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Investments - Additional Information (Detail) (USD $)
In Thousands, unless otherwise specified
12 Months Ended 3 Months Ended
Dec. 31, 2014
Mar. 31, 2015
Mar. 31, 2014
Investment [Line Items]      
Payment of permitted policy claim (percent) 25.00%ambc_PaymentAsPercentageOfPermittedPolicyClaim    
Future payment of permitted policy claim (percent) 45.00%ambc_CurrentPaymentasaPercentageofPermittedPolicyClaim    
Securities fair value $ 6,790ambc_FairValueOfSecuritiesDepositedWithGovernmentalAuthorities $ 6,842ambc_FairValueOfSecuritiesDepositedWithGovernmentalAuthorities  
Successor [Member]      
Investment [Line Items]      
Unrealized losses on securities 20,081us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
22,671us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
 
Other investments   9,651ambc_OtherInvestmentsIncome
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
1,994ambc_OtherInvestmentsIncome
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments 32,269us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
29,363us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
 
Below Investment Grade Securities and Non-Rated Securities [Member] | Successor [Member]      
Investment [Line Items]      
Fair value of below investment grade securities and non-rated securities 473,656ambc_BelowInvestmentGradeSecuritiesAndNonRatedSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ambc_BelowInvestmentGradeSecuritiesAndNonRatedSecuritiesMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
613,511ambc_BelowInvestmentGradeSecuritiesAndNonRatedSecuritiesContinuousUnrealizedLossPositionFairValue
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ambc_BelowInvestmentGradeSecuritiesAndNonRatedSecuritiesMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
 
Gross unrealized loss 16,001ambc_BelowInvestmentGradeSecuritiesAndNonRatedSecuritiesContinuousUnrealizedLossPositionAggregateLosses
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ambc_BelowInvestmentGradeSecuritiesAndNonRatedSecuritiesMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
20,130ambc_BelowInvestmentGradeSecuritiesAndNonRatedSecuritiesContinuousUnrealizedLossPositionAggregateLosses
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ambc_BelowInvestmentGradeSecuritiesAndNonRatedSecuritiesMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
 
Residential Mortgage-Backed Securities [Member] | Successor [Member]      
Investment [Line Items]      
Unrealized losses on securities 12,391us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
   
Ambac Wrapped Securities [Member] | Successor [Member]      
Investment [Line Items]      
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments   16,631us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ambc_AmbacWrappedSecuritiesMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
 
Asset-backed Securities [Member] | Successor [Member]      
Investment [Line Items]      
Unrealized losses on securities 155us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_AssetBackedSecuritiesMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
   
Gains (losses) on securities held as of reporting date [Member] | Successor [Member]      
Investment [Line Items]      
Other investments   6,255ambc_OtherInvestmentsIncome
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ambc_GainslossesonsecuritiesheldasofreportingdateMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
2,449ambc_OtherInvestmentsIncome
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ambc_GainslossesonsecuritiesheldasofreportingdateMember
/ us-gaap_StatementScenarioAxis
= us-gaap_SuccessorMember
National Century Financial Enterprises, Inc. [Member]      
Investment [Line Items]      
Cash recoveries $ 35us-gaap_LitigationSettlementAmount
/ dei_LegalEntityAxis
= ambc_NationalCenturyFinancialEnterprisesIncMember
$ 0us-gaap_LitigationSettlementAmount
/ dei_LegalEntityAxis
= ambc_NationalCenturyFinancialEnterprisesIncMember