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Financial Guarantee Insurance Contracts - Summary of Rollforward of RMBS Subrogation, by Estimation Approach (Detail) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2012 Transactions
Summary Of Rollforward Of Rmbs Subrogation By Estimation Approach [Line Items] |
Discounted RMBS subrogation (gross of reinsurance) at January 1, 2012 | $ 2,720,266
Additional transactions reviewed | 18,981
Additional adverse sample loans reviewed |
Adverse loans repurchased by the sponsor | 35
All other changes | (216,057)
Discounted RMBS subrogation (gross of reinsurance) at December 31, 2012 | 2,523,225
Discounted RMBS subrogation (gross of reinsurance) at January 1, 2012 | 46
Discounted RMBS subrogation (gross of reinsurance) at December 31, 2012 | 49
Random samples [Member] |
Summary Of Rollforward Of Rmbs Subrogation By Estimation Approach [Line Items] |
Discounted RMBS subrogation (gross of reinsurance) at January 1, 2012 | 1,262,794
Additional transactions reviewed | 54,467
Additional adverse sample loans reviewed |
Adverse loans repurchased by the sponsor |
All other changes | (236,853)
Discounted RMBS subrogation (gross of reinsurance) at December 31, 2012 | 1,080,408
Discounted RMBS subrogation (gross of reinsurance) at January 1, 2012 | 16
Additional transactions reviewed | 6
All other changes |
Discounted RMBS subrogation (gross of reinsurance) at December 31, 2012 | 22
Adverse samples [Member] |
Summary Of Rollforward Of Rmbs Subrogation By Estimation Approach [Line Items] |
Discounted RMBS subrogation (gross of reinsurance) at January 1, 2012 | 1,457,472
Additional transactions reviewed | (35,486)
Additional adverse sample loans reviewed |
Adverse loans repurchased by the sponsor | 35
All other changes | 20,796
Discounted RMBS subrogation (gross of reinsurance) at December 31, 2012 | $ 1,442,817
Discounted RMBS subrogation (gross of reinsurance) at January 1, 2012 | 30
Additional transactions reviewed | (1)
All other changes | (2)
Discounted RMBS subrogation (gross of reinsurance) at December 31, 2012 | 27

X
- Definition This element represents the change in RMBS subrogation due to additional adverse sample loans reviewed. + References No definition available. + Details
Name: | abk_AdditionalAdverseSampleLoansReviewedChangeInRmbsSubrogation
Namespace Prefix: | abk_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition This element represents the change in subrogation due to additional transactions reviewed. + References No definition available. + Details
Name: | abk_AdditionalTransactionsReviewedChangesInRmbsSubrogation
Namespace Prefix: | abk_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition This element represents the change in Rmbs subrogation due to adverse loans repurchased by sponsor. + References No definition available. + Details
Name: | abk_AdverseLoansRepurchasedBySponsorChangeInRmbsSubrogation
Namespace Prefix: | abk_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Number Of Additional Rmbs Transactions Reviewed With Potential Recoveries + References No definition available. + Details
Name: | abk_NumberOfAdditionalRmbsTransactionsReviewedWithPotentialRecoveries
Namespace Prefix: | abk_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number of total remediation transactions. + References No definition available. + Details
Name: | abk_NumberOfRemediationTransactions
Namespace Prefix: | abk_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition This element represents the changes in RMBS subrogation for reasons other than additional transactions being reviewed, adverse loans being reviewed or due to adverse loans being repurchased by the sponsor. + References No definition available. + Details
Name: | abk_OtherChangesRmbsSubrogation
Namespace Prefix: | abk_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Other Changes Rmbs Subrogation Number Of Transactions + References No definition available. + Details
Name: | abk_OtherChangesRmbsSubrogationNumberOfTransactions
Namespace Prefix: | abk_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Schedule Of Insured Financial Obligations With Credit Deterioration Reductions Of Gross Claim Liability Subrogation Rmbs + References No definition available. + Details
Name: | abk_ScheduleOfInsuredFinancialObligationsWithCreditDeteriorationReductionsOfGrossClaimLiabilitySubrogationRmbs
Namespace Prefix: | abk_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | abk_SummaryOfRollforwardOfRmbsSubrogationByEstimationApproachLineItems
Namespace Prefix: | abk_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration