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Investments - Summary of Fair Value, Including Financial Guarantee, and Weighted-Average Underlying Rating, Excluding Financial Guarantee, of Insured Securities (Detail) (Successor [Member], USD $) In Thousands, unless otherwise specified | Mar. 31, 2015 | Dec. 31, 2014
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Standard & Poor's, CCC- Rating [Member] | Ambac Assurance Corporation [Member] |  |
Investment [Line Items] |  |
Fair value of securities that include benefit of guarantees provided by financial guarantors | $ 2,132,208 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsCCCMinusRatingMember / invest_InvestmentAxis = ambc_AmbacAssuranceCorporationMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | $ 2,199,719 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsCCCMinusRatingMember / invest_InvestmentAxis = ambc_AmbacAssuranceCorporationMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember
Standard & Poor's, A Rating [Member] | Assured Guaranty Municipal Corporation [Member] |  |
Investment [Line Items] |  |
Fair value of securities that include benefit of guarantees provided by financial guarantors | 121,519 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsARatingMember / invest_InvestmentAxis = ambc_AssuredGuarantyMunicipalCorporationMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 119,492 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsARatingMember / invest_InvestmentAxis = ambc_AssuredGuarantyMunicipalCorporationMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember
Standard & Poor's, A- Rating [Member] | National Public Finance Guarantee Corporation [Member] |  |
Investment [Line Items] |  |
Fair value of securities that include benefit of guarantees provided by financial guarantors | 64,693 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsAMinusRatingMember / invest_InvestmentAxis = ambc_NationalPublicFinanceGuaranteeCorporationMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 67,895 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsAMinusRatingMember / invest_InvestmentAxis = ambc_NationalPublicFinanceGuaranteeCorporationMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember
Standard & Poor's, A+ Rating [Member] | MBIA Insurance Corporation [Member] |  |
Investment [Line Items] |  |
Fair value of securities that include benefit of guarantees provided by financial guarantors | 32,265 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsAPlusRatingMember / invest_InvestmentAxis = ambc_MbiaInsuranceCorporationMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 32,460 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsAPlusRatingMember / invest_InvestmentAxis = ambc_MbiaInsuranceCorporationMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember
Standard & Poor's, CCC Rating [Member] |  |
Investment [Line Items] |  |
Fair value of securities that include benefit of guarantees provided by financial guarantors | 2,350,685 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsCCCRatingMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 2,419,566 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsCCCRatingMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember
Municipal Bonds [Member] | Standard & Poor's, CCC- Rating [Member] | Ambac Assurance Corporation [Member] |  |
Investment [Line Items] |  |
Fair value of securities that include benefit of guarantees provided by financial guarantors | 54,124 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsCCCMinusRatingMember / us-gaap_GuaranteeObligationsByNatureAxis = us-gaap_MunicipalBondsMember / invest_InvestmentAxis = ambc_AmbacAssuranceCorporationMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 53,164 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsCCCMinusRatingMember / us-gaap_GuaranteeObligationsByNatureAxis = us-gaap_MunicipalBondsMember / invest_InvestmentAxis = ambc_AmbacAssuranceCorporationMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember
Municipal Bonds [Member] | Standard & Poor's, A Rating [Member] | Assured Guaranty Municipal Corporation [Member] |  |
Investment [Line Items] |  |
Fair value of securities that include benefit of guarantees provided by financial guarantors | 121,519 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsARatingMember / us-gaap_GuaranteeObligationsByNatureAxis = us-gaap_MunicipalBondsMember / invest_InvestmentAxis = ambc_AssuredGuarantyMunicipalCorporationMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 119,492 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsARatingMember / us-gaap_GuaranteeObligationsByNatureAxis = us-gaap_MunicipalBondsMember / invest_InvestmentAxis = ambc_AssuredGuarantyMunicipalCorporationMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember
Municipal Bonds [Member] | Standard & Poor's, A- Rating [Member] | National Public Finance Guarantee Corporation [Member] |  |
Investment [Line Items] |  |
Fair value of securities that include benefit of guarantees provided by financial guarantors | 64,693 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsAMinusRatingMember / us-gaap_GuaranteeObligationsByNatureAxis = us-gaap_MunicipalBondsMember / invest_InvestmentAxis = ambc_NationalPublicFinanceGuaranteeCorporationMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 67,895 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsAMinusRatingMember / us-gaap_GuaranteeObligationsByNatureAxis = us-gaap_MunicipalBondsMember / invest_InvestmentAxis = ambc_NationalPublicFinanceGuaranteeCorporationMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember
Municipal Bonds [Member] | Standard & Poor's, CCC Rating [Member] |  |
Investment [Line Items] |  |
Fair value of securities that include benefit of guarantees provided by financial guarantors | 240,336 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsCCCRatingMember / us-gaap_GuaranteeObligationsByNatureAxis = us-gaap_MunicipalBondsMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 240,551 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsCCCRatingMember / us-gaap_GuaranteeObligationsByNatureAxis = us-gaap_MunicipalBondsMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember
Corporate Debt Securities [Member] | Standard & Poor's, A Rating [Member] | Assured Guaranty Municipal Corporation [Member] |  |
Investment [Line Items] |  |
Fair value of securities that include benefit of guarantees provided by financial guarantors | 0 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsARatingMember / us-gaap_GuaranteeObligationsByNatureAxis = us-gaap_CorporateDebtSecuritiesMember / invest_InvestmentAxis = ambc_AssuredGuarantyMunicipalCorporationMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 0 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsARatingMember / us-gaap_GuaranteeObligationsByNatureAxis = us-gaap_CorporateDebtSecuritiesMember / invest_InvestmentAxis = ambc_AssuredGuarantyMunicipalCorporationMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember
Corporate Debt Securities [Member] | Standard & Poor's, A- Rating [Member] | National Public Finance Guarantee Corporation [Member] |  |
Investment [Line Items] |  |
Fair value of securities that include benefit of guarantees provided by financial guarantors | 0 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsAMinusRatingMember / us-gaap_GuaranteeObligationsByNatureAxis = us-gaap_CorporateDebtSecuritiesMember / invest_InvestmentAxis = ambc_NationalPublicFinanceGuaranteeCorporationMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 0 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsAMinusRatingMember / us-gaap_GuaranteeObligationsByNatureAxis = us-gaap_CorporateDebtSecuritiesMember / invest_InvestmentAxis = ambc_NationalPublicFinanceGuaranteeCorporationMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember
Corporate Debt Securities [Member] | Standard & Poor's, A+ Rating [Member] | MBIA Insurance Corporation [Member] |  |
Investment [Line Items] |  |
Fair value of securities that include benefit of guarantees provided by financial guarantors | 32,265 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsAPlusRatingMember / us-gaap_GuaranteeObligationsByNatureAxis = us-gaap_CorporateDebtSecuritiesMember / invest_InvestmentAxis = ambc_MbiaInsuranceCorporationMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 32,460 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsAPlusRatingMember / us-gaap_GuaranteeObligationsByNatureAxis = us-gaap_CorporateDebtSecuritiesMember / invest_InvestmentAxis = ambc_MbiaInsuranceCorporationMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember
Corporate Debt Securities [Member] | Standard & Poor's, CCC Rating [Member] |  |
Investment [Line Items] |  |
Fair value of securities that include benefit of guarantees provided by financial guarantors | 32,265 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsCCCRatingMember / us-gaap_GuaranteeObligationsByNatureAxis = us-gaap_CorporateDebtSecuritiesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 32,460 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsCCCRatingMember / us-gaap_GuaranteeObligationsByNatureAxis = us-gaap_CorporateDebtSecuritiesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember
Mortgage and Asset-Backed Securities [Member] | Standard & Poor's, CCC- Rating [Member] | Ambac Assurance Corporation [Member] |  |
Investment [Line Items] |  |
Fair value of securities that include benefit of guarantees provided by financial guarantors | 2,078,084 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsCCCMinusRatingMember / us-gaap_GuaranteeObligationsByNatureAxis = ambc_MortgageAndOtherAssetBackedSecuritiesMember / invest_InvestmentAxis = ambc_AmbacAssuranceCorporationMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | 2,146,555 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsCCCMinusRatingMember / us-gaap_GuaranteeObligationsByNatureAxis = ambc_MortgageAndOtherAssetBackedSecuritiesMember / invest_InvestmentAxis = ambc_AmbacAssuranceCorporationMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember
Mortgage and Asset-Backed Securities [Member] | Standard & Poor's, CCC Rating [Member] |  |
Investment [Line Items] |  |
Fair value of securities that include benefit of guarantees provided by financial guarantors | $ 2,078,084 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsCCCRatingMember / us-gaap_GuaranteeObligationsByNatureAxis = ambc_MortgageAndOtherAssetBackedSecuritiesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember | $ 2,146,555 us-gaap_InvestmentOwnedAtFairValue / invest_CreditRatingSourceAxis = us-gaap_StandardPoorsCCCRatingMember / us-gaap_GuaranteeObligationsByNatureAxis = ambc_MortgageAndOtherAssetBackedSecuritiesMember / us-gaap_StatementScenarioAxis = us-gaap_SuccessorMember

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- Definition Value of the investment at close of period. For schedules of investments that are categorized, the value would be aggregated by category. For investment in and advances to affiliates, if operations of any controlled companies are different in character from those of the company, group such affiliates within divisions and by type of activities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 13 -Paragraph Column C -Article 12 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 14 -Paragraph Column E -Article 12 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 1 -Subparagraph (SX 210.12-12.Column C.3,4) -URI http://asc.fasb.org/extlink&oid=34726532&loc=d3e611133-123010 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-12C.Column C.7) -URI http://asc.fasb.org/extlink&oid=34726532&loc=d3e611225-123010 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 6 -Subparagraph (SX 210.12-14.Column E.2,3) -URI http://asc.fasb.org/extlink&oid=34726532&loc=d3e611322-123010 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 5 -Subparagraph (SX 210.12-13.Column C.6) -URI http://asc.fasb.org/extlink&oid=34726532&loc=d3e611282-123010 Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 12 -Paragraph Column C -Article 12 Reference 8: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 12 -Paragraph 3, 4 -Article 12 Reference 9: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 14 -Paragraph 2, 3 -Article 12 Reference 10: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 13 -Paragraph 6 -Article 12 Reference 11: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 12C -Paragraph 7 -Article 12 Reference 12: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 12C -Paragraph Column C -Article 12 + Details
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