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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 | $ 6,790 ambc_FairValueOfSecuritiesDepositedWithGovernmentalAuthorities | $ 6,842 ambc_FairValueOfSecuritiesDepositedWithGovernmentalAuthorities |
Successor [Member] |  |  |
Investment [Line Items] |  |  |
Unrealized losses on securities | 20,081 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 22,671 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember |
Other investments |  | 9,651 ambc_OtherInvestmentsIncome / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 1,994 ambc_OtherInvestmentsIncome / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 32,269 us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 29,363 us-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 | 473,656 ambc_BelowInvestmentGradeSecuritiesAndNonRatedSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ambc_BelowInvestmentGradeSecuritiesAndNonRatedSecuritiesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 613,511 ambc_BelowInvestmentGradeSecuritiesAndNonRatedSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ambc_BelowInvestmentGradeSecuritiesAndNonRatedSecuritiesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember |
Gross unrealized loss | 16,001 ambc_BelowInvestmentGradeSecuritiesAndNonRatedSecuritiesContinuousUnrealizedLossPositionAggregateLosses / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ambc_BelowInvestmentGradeSecuritiesAndNonRatedSecuritiesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 20,130 ambc_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 | 12,391 us-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 |  | 16,631 us-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 | 155 us-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 |  | 6,255 ambc_OtherInvestmentsIncome / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ambc_GainslossesonsecuritiesheldasofreportingdateMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 2,449 ambc_OtherInvestmentsIncome / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ambc_GainslossesonsecuritiesheldasofreportingdateMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember
National Century Financial Enterprises, Inc. [Member] |  |  |
Investment [Line Items] |  |  |
Cash recoveries | $ 35 us-gaap_LitigationSettlementAmount / dei_LegalEntityAxis = ambc_NationalCenturyFinancialEnterprisesIncMember | $ 0 us-gaap_LitigationSettlementAmount / dei_LegalEntityAxis = ambc_NationalCenturyFinancialEnterprisesIncMember |

X
- Definition Aggregate losses of below investment grade securities and non rated securities in a continuous unrealized loss position. + References No definition available. + Details
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- Definition Fair value of below investment grade securities and non rated securities in a continuous unrealized loss position. + References No definition available. + Details
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X
- Definition Percentage of the Segregated Account of Ambac Assurance's permitted policy claims that are to be paid in cash from July 2014 forward as approved by the Rehabilitation Court. + References No definition available. + Details
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- Definition Fair value of securities deposited with governmental authorities. + References No definition available. + Details
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- Definition Percentage of the Segregated Account of Ambac Assurance's permitted policy claims that were paid in cash from September 2012 through June 2014. + References No definition available. + Details
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- Definition Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563 + Details
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- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563 + Details
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- Definition Amount of judgment or settlement awarded to (against) the entity in respect of litigation. + References No definition available. + Details
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