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Net Premiums Earned - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2012 | Sep. 30, 2011 | Sep. 30, 2012 | Sep. 30, 2011 | Dec. 31, 2011
Weighted average risk-free rate |  |  | 2.60% |  | 2.60%
Weighted average period of future premiums |  |  | 10 years 5 months |  | 10 years
Transactions with non-investment grade internal ratings |  |  | 43.00% |  | 43.00%
Non-investment grade MBS |  |  | 9.00% |  | 12.00%
Student loan transactions |  |  | 11.00% |  | 11.00%
Premium receivables uncollectible and written off relating to a non-investment grade obligation |  |  | $ 106,714 |  | $ 90,930
Premium receivables uncollectible relating to a non-investment grade obligation | 15,784 |  | 15,784 |  |
Past due premiums on policies insuring non-investment grade obligations | 500 |  | 500 |  |
Accelerated premium revenue for retired obligations | $ 34,381 | $ 18,835 | $ 86,037 | $ 30,096 |

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- Definition Percentage of premiums receivable related to non investment grade RMBS transactions. + References No definition available. + Details
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- Definition Percentage of premiums receivable related to student loan transactions. + References No definition available. + Details
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Data Type: | num:percentItemType
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- Definition Percentage premiums receivable related to transactions with non-investment grade internal ratings. + References No definition available. + Details
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- Definition Past due premiums receivable not written off related to non-investment grade obligation. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
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- Definition Premiums deemed uncollectible and written off related to non-investment grade obligation. + References No definition available. + Details
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- Definition Premiums deemed uncollectible related to non-investment grade obligation. + References No definition available. + Details
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Namespace Prefix: | abk_
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Balance Type: | debit
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- 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
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- 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
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- Definition This element represents the weighted average risk free rate used to discount the premiums expected to be collected for financial guarantee insurance contracts where the premium is to be received over the contract period. + 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)(4) -URI http://asc.fasb.org/extlink&oid=6933075&loc=SL5748726-161290 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 163 -Paragraph 30 -Subparagraph a(3) -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
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