Insurance [Line Items]

No definition available.

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Namespace Prefix:	ambc_
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Balance Type:	na
Period Type:	duration

- Definition

Amount of increase (decrease) in allowance for credit loss on accounts receivable.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919249-210447

+ Details

Name:	us-gaap_AllowanceForDoubtfulAccountsReceivablePeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
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://fasb.org/us-gaap/role/ref/legacyRef
-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

+ Details

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

- Definition

Amount of the premium receivable for financial guarantee insurance contracts reported in the statement of financial position. This element primarily would consist of those financial guarantee insurance contracts which premiums are to be collected over the contract period, but may, on occasion, include premiums which are to be collected in full at inception, but which straddle a financial reporting period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 310
-Section 50
-Paragraph 3
-Subparagraph (c)(1),(5)
-URI http://asc.fasb.org/extlink&oid=6933075&loc=SL5748726-161290

+ Details

Name:	us-gaap_FinancialGuaranteeInsuranceContractsPremiumReceivable
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of cash inflow from premiums received for premium receivable on financial guarantee insurance contracts.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 17
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3367-108585

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 310
-Section 50
-Paragraph 3
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=6933075&loc=SL5748726-161290

+ Details

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

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

Name:	us-gaap_FinancialGuaranteeInsuranceContractsPremiumReceivableRollForward
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of accretion of the discount for premiums receivable on financial guarantee insurance contracts.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 310
-Section 50
-Paragraph 3
-Subparagraph (c)(4)(iii)
-URI http://asc.fasb.org/extlink&oid=6933075&loc=SL5748726-161290

+ Details

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

- Definition

Amount of increase (decrease) in the premium receivable on financial guarantee insurance contracts from changes in the period of the contract.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 310
-Section 50
-Paragraph 3
-Subparagraph (c)(4)(i)
-URI http://asc.fasb.org/extlink&oid=6933075&loc=SL5748726-161290

+ Details

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

- Definition

Amount of increase (decrease) in the premiums receivable on financial guarantee insurance contracts from adjustments classified as other.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 310
-Section 50
-Paragraph 3
-Subparagraph (c)(4)(iv)
-URI http://asc.fasb.org/extlink&oid=6933075&loc=SL5748726-161290

+ Details

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

- Definition

The carrying value as of the balance sheet date of the estimated valuation allowance to reduce gross premiums receivable to net realizable value.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(5))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919249-210447

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919249-210447

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-Publisher FASB
-Name Accounting Standards Codification
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+ Details

Name:	us-gaap_PremiumsReceivableAllowanceForDoubtfulAccounts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

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Financial Guarantee Insurance Contracts - Summary of Gross Premium Receivable Roll-Forward (Direct and Assumed Contracts) (Detail) € in Thousands, £ in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2018 EUR (€)	Jun. 30, 2018 GBP (£)	Jun. 30, 2019 USD ($)	Jun. 30, 2019 EUR (€)	Jun. 30, 2019 GBP (£)	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Insurance [Line Items]
Financial Guarantee Insurance Contracts, Accelerated Premium Revenue, Amount	$ (6,169)	$ 6,103			$ 6,054			$ 15,495
Financial Guarantee Insurance Contracts, Premium Receivable [Roll Forward]
Beginning premium receivable					495,391			586,312
Premium receipts					25,693			29,822
Adjustments for changes in expected and contractual cash flows					(22,310)			(5,066)
Accretion of premium receivable discount					6,206			7,627
Uncollectable premiums					(1,155)			(11)
Other adjustments (including foreign exchange)					(10,913)			(5,082)
Ending premium receivable	441,526	553,958			441,526			553,958
Premium Receivable, Allowance for Credit Loss	8,288				8,288				$ 7,136
United Kingdom, Pounds
Financial Guarantee Insurance Contracts, Premium Receivable [Roll Forward]
Ending premium receivable	137,137	151,316		£ 114,729	137,137		£ 107,974	151,316
Euro Member Countries, Euro
Financial Guarantee Insurance Contracts, Premium Receivable [Roll Forward]
Ending premium receivable	$ 28,367	$ 33,114	€ 28,380		$ 28,367	€ 24,941		$ 33,114