Accumulated amount of amortization on insurance intangible asset.

No definition available.

Name:	ambc_AccumulatedAmortizationOnInsuranceIntangibleAsset
Namespace Prefix:	ambc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This element represents the reduction to gross claim liability for subrogation on insured RMBS financial obligations with credit deterioration.

+ References

No definition available.

+ Details

Name:	ambc_BalanceOfGrossRmbsSubrogationRecoveries
Namespace Prefix:	ambc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This element represents the reduction to gross claim liability for subrogation on insured RMBS financial obligations with credit deterioration, net of reinsurance.

+ References

No definition available.

+ Details

Name:	ambc_BalanceOfRmbsSubrogationRecoveriesNetOfReinsurance
Namespace Prefix:	ambc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Financial Guarantee Insurance Contracts Premium Receivable Deemed Uncollectible

+ References

No definition available.

+ Details

Name:	ambc_FinancialGuaranteeInsuranceContractsPremiumReceivableDeemedUncollectible
Namespace Prefix:	ambc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The known and estimated amount recoverable as of the balance sheet date from reinsurers for claims paid or incurred by the ceding insurer.

+ References

No definition available.

+ Details

Name:	ambc_LossReservesCededToReinsurers
Namespace Prefix:	ambc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Percentage of financial guarantee premiums receivable related to RMBS insured transactions with non-investment grade internal ratings.

+ References

No definition available.

+ Details

Name:	ambc_PercentageOfPremiumsReceivableRelatedToNonInvestmentGradeRmbsTransactions
Namespace Prefix:	ambc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of financial guarantee premiums receivable related to Student Loan insured transactions with non-investment grade internal ratings.

+ References

No definition available.

+ Details

Name:	ambc_PercentageOfPremiumsReceivableRelatedToStudentLoanTransactions
Namespace Prefix:	ambc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage Premiums Receivable Related To Asset Backed Transactions

+ References

No definition available.

+ Details

Name:	ambc_PercentagePremiumsReceivableRelatedToAssetBackedTransactions
Namespace Prefix:	ambc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of financial guarantee premiums receivable related to insured transactions with non-investment grade internal ratings.

+ References

No definition available.

+ Details

Name:	ambc_PercentagePremiumsReceivableRelatedToTransactionsWithNonInvestmentGradeInternalRatings
Namespace Prefix:	ambc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Past due premiums on policies insuring internally rated non-investment grade obligations.

+ References

No definition available.

+ Details

Name:	ambc_PremiumsPastDueOnNonInvestmentGradeObligation
Namespace Prefix:	ambc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Loss adjustment expense reserves, net of reinsurance, represent the costs estimated to be incurred in the settlement of unpaid claims.

+ References

No definition available.

+ Details

Name:	ambc_ReserveForLossAdjustmentExpenses
Namespace Prefix:	ambc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	ambc_UnpaidLossesAndLossExpensesLineItems
Namespace Prefix:	ambc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The weighted average amortization period of insurance intangible asset.

+ References

No definition available.

+ Details

Name:	ambc_WeightedAverageIntangibleAmortizationPeriod
Namespace Prefix:	ambc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16225-109274

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (a)(2)

-URI http://asc.fasb.org/extlink&oid=7658586&loc=d3e16323-109275

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 142

-Paragraph 45

-Subparagraph a(2)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Name:	us-gaap_AmortizationOfIntangibleAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents the amount of premium revenue on financial guarantee insurance contracts recognized during the period that was accelerated for revenue recognition purposes.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 605

-Section 50

-Paragraph 4

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6933581&loc=SL5749298-161291

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 163

-Paragraph 30

-Subparagraph d

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Name:	us-gaap_FinancialGuaranteeInsuranceContractsAcceleratedPremiumRevenueAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This element represents the weighted average risk free rate used to discount the claim liability related to financial guarantee insurance contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 40

-Section 50

-Paragraph 9

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6933314&loc=SL5749324-161292

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 163

-Paragraph 30

-Subparagraph f(1)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Name:	us-gaap_FinancialGuaranteeInsuranceContractsClaimLiabilityWeightedAverageRiskFreeDiscountRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted average period over which premium receivable for financial guarantee insurance contracts is collected where premium is received over the contract period, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 310

-Section 50

-Paragraph 3

-Subparagraph (a)(5)

-URI http://asc.fasb.org/extlink&oid=6933075&loc=SL5748726-161290

+ Details

Name:	us-gaap_FinancialGuaranteeInsuranceContractsPremiumReceivedOverContractPeriodPremiumReceivableWeightedAverageCollectionPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The reduction in the amount of the provision for the period for claims and benefits incurred on contract risks ceded to other insurers under reinsurance arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 20

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6480758&loc=d3e6811-158387

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 113

-Paragraph 27, 113

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Name:	us-gaap_ReinsuranceEffectOnClaimsAndBenefitsIncurredAmountCeded
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Financial Guarantee Insurance Contracts - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended	2 Months Ended	1 Months Ended	3 Months Ended	4 Months Ended	6 Months Ended		2 Months Ended	6 Months Ended		12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Successor Ambac [Member]	Apr. 30, 2013 Predecessor Ambac [Member]	Jun. 30, 2012 Predecessor Ambac [Member]	Apr. 30, 2013 Predecessor Ambac [Member]	Jun. 30, 2012 Predecessor Ambac [Member]	Jun. 30, 2013 Insurance Intangible Asset [Member]	Jun. 30, 2013 Insurance Intangible Asset [Member] Successor Ambac [Member]	Jun. 30, 2013 Maximum [Member]	Jun. 30, 2013 Loss Reserves [Member]	Dec. 31, 2012 Loss Reserves [Member]
Unpaid Losses And Loss Expenses [Line Items]
Weighted average risk-free interest rate	2.80%	2.60%									2.70%	1.60%
Weighted average period of future premiums	10 years	9 years 7 months 6 days
Transactions with non-investment grade internal ratings	40.00%	40.00%
Non-investment grade RMBS on total premiums receivable	7.00%	7.00%
Percentage of student loan transactions on total premium receivables	9.00%	9.00%
Percentage related to asset-backed transaction	15.00%	15.00%
Premium receivables relating to a non-investment obligation deemed uncollectible		$ 118,961
Past due premiums on policies insuring non-investment grade obligations amount										500
Accelerated premium revenue for retired obligations			13,049	7,073	35,866	36,433	51,656
Total net loss expense reserves	113,185	136,790
Reinsurance recoveries of losses included in losses and loss expenses			5,396	7	9,334	3,889	21,852
Losses and loss expense reserves ceded to reinsurers	142,512	147,409
Subrogation recoveries	2,394,933	2,523,225
Subrogation recoveries, net of reinsurance	2,369,005	2,497,233
Weighted-average amortization period								9 years 4 months 24 days
Intangible amortization expense			24,952						24,952
Accumulated amortization on insurance intangible asset									$ 24,952