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Investments - Summary of Sources of Collateral Received and Various Investment Agreement in which Collateral Pledged (Detail) (Cash And Securities Pledged Directly From The Investment Portfolio [Member], USD $) | Sep. 30, 2012 | Dec. 31, 2011
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Cash And Securities Pledged Directly From The Investment Portfolio [Member] |  |
Fair Value of Cash and Underlying Securities | $ 735,229 | $ 874,987
Fair Value of Cash and Securities Pledged to Investment and Repurchase Agreement Counterparties | 432,592 | 564,036
Fair Value of Cash and Securities Pledged to Derivative Counterparties | $ 302,637 | $ 310,951

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- Definition Fair value of cash and securities pledged to derivative counterparties. + References No definition available. + Details
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Namespace Prefix: | abk_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Fair value of cash and securities pledged to investment and repurchase agreement counterparties. + References No definition available. + Details
Name: | abk_FairValueOfCashAndSecuritiesPledgedToInvestmentAndRepurchaseAgreementCounterparties
Namespace Prefix: | abk_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Total fair value of cash and underlying securities pledged. + References No definition available. + Details
Name: | abk_FairValueOfCashAndUnderlyingSecurities
Namespace Prefix: | abk_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant