XML 80 R61.htm IDEA: XBRL DOCUMENT v3.19.1

Fair Value Measurements - Summary of Information about Described Model Inputs Used to Determine Fair Value of Each Class of Credit Derivatives (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Other investments	$ 428,556	$ 391,217
Fair value of derivative liabilities	73,510
Real Estate [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Other investments	16,150	16,123
Interest Rate Contract [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Other investments	207,704	177,357
Illiquid Investments [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Other investments	$ 85,323	$ 84,297
Asset-backed Securities [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Inputs Coupon Rate	5.97%	5.97%
Fair Value Inputs Maturity	16 years 1 month 9 days	16 years 3 months 14 days
Fair Value Inputs Yield	12.00%	12.00%
Variable Interest Entity, Primary Beneficiary [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair value of derivative liabilities	$ 0
Variable Interest Entity, Primary Beneficiary [Member] | European Transactions [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Fair Value Inputs Coupon Rate	2.20%	2.20%
Fair Value Inputs Maturity	18 years 8 months 4 days	18 years 11 months 4 days
Fair Value Inputs Yield	3.05%	3.18%

X

- Definition

Fair value inputs coupon rate.

+ References

No definition available.

+ Details

Name:	ambc_FairValueInputsCouponRate
Namespace Prefix:	ambc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Fair value inputs maturity.

+ References

No definition available.

+ Details

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

X

- Definition

Fair value inputs yield.

+ References

No definition available.

+ Details

Name:	ambc_FairValueInputsYield
Namespace Prefix:	ambc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Fair value, after offset of derivative asset, of financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, elected not to be and before offset against a right to receive collateral under a master netting arrangement. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=d3e41678-113959

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226006-175313

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313

+ Details

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

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

X

- Definition

Amount of investments classified as other.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(f,g))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

X

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_RealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_InterestRateContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_InvestmentTypeAxis=ambc_IlliquidInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FairValueByAssetClassAxis=ambc_EuropeanTransactionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: