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Investments - Summary of Net Investment Income (Detail) (Successor [Member], USD $) In Thousands, unless otherwise specified | 3 Months Ended
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Mar. 31, 2015 | Mar. 31, 2014
Investment [Line Items] |  |
Net Realized and Unrealized Gain (Loss) on Trading Securities | $ 7,819 us-gaap_NetRealizedOrUnrealizedGainLossOnTradingSecurities | $ 1,994 us-gaap_NetRealizedOrUnrealizedGainLossOnTradingSecurities
Trading Securities, Realized Gain (Loss) | 1,564 us-gaap_TradingSecuritiesRealizedGainLoss | (455)us-gaap_TradingSecuritiesRealizedGainLoss
Fixed income securities | 65,585 ambc_InvestmentIncomeInterestOnDebtSecurities | 71,231 ambc_InvestmentIncomeInterestOnDebtSecurities
Short-term investments | 42 ambc_InvestmentIncomeInsuranceEntityShortTermInvestments | 57 ambc_InvestmentIncomeInsuranceEntityShortTermInvestments
Loans | 132 ambc_InvestmentIncomeInterestOnLoansReceivable | 117 ambc_InvestmentIncomeInterestOnLoansReceivable
Investment expense | (2,427)us-gaap_InvestmentIncomeInvestmentExpense | (2,598)us-gaap_InvestmentIncomeInvestmentExpense
Securities available-for-sale and short-term | 63,332 us-gaap_InterestAndDividendIncomeSecuritiesAvailableForSale | 68,807 us-gaap_InterestAndDividendIncomeSecuritiesAvailableForSale
Other investments | 9,651 ambc_OtherInvestmentsIncome | 1,994 ambc_OtherInvestmentsIncome
Total net investment income | 72,983 us-gaap_NetInvestmentIncome | 70,801 us-gaap_NetInvestmentIncome
Gains (losses) on securities held as of reporting date [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

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- Definition Amount of operating dividend and interest income, including amortization and accretion of premiums and discounts, on available-for-sale securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Available-for-Sale Securities -URI http://asc.fasb.org/extlink&oid=6505594 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.2) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 2 -Article 9 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 35 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e24721-111560 + Details
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- Definition Amount of expenses related to the generation of investment income. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.2) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.9) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 + Details
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- Definition Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 16 -Article 12 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.2) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 2 -Article 7 + Details
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- Definition The sum of the realized and unrealized net gain (loss) on trading securities during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Trading Securities -URI http://asc.fasb.org/extlink&oid=6526789 + Details
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- Definition This item represents the gain (loss) realized during the period from the sale of trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 7 -Subparagraph c -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.7(c)) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Trading Securities -URI http://asc.fasb.org/extlink&oid=6526789 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563 + Details
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