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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

X

- Definition

Percentage of premiums receivable related to non investment grade RMBS transactions.

+ References

No definition available.

+ Details

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X

- Definition

Percentage of premiums receivable related to student loan transactions.

+ References

No definition available.

+ Details

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Namespace Prefix:	abk_
Data Type:	num:percentItemType
Balance Type:	na
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X

- Definition

Percentage premiums receivable related to transactions with non-investment grade internal ratings.

+ References

No definition available.

+ Details

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Namespace Prefix:	abk_
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X

- Definition

Past due premiums receivable not written off related to non-investment grade obligation.

+ References

No definition available.

+ Details

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Namespace Prefix:	abk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Premiums deemed uncollectible and written off related to non-investment grade obligation.

+ References

No definition available.

+ Details

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X

- 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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X

- 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.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- 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

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Namespace Prefix:	us-gaap_
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Balance Type:	na
Period Type:	duration

X

- 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.

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