v2.4.0.6

Recent Accounting Pronouncements - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended
--- | --- | --- | --- | ---
Sep. 30, 2012 | Sep. 30, 2012 | Sep. 30, 2011 | Sep. 30, 2011 Accounting Standards Update 2010-26 | Sep. 30, 2011 Accounting Standards Update 2010-26 | Sep. 30, 2012 Minimum Accounting Standards Update 2010-26 | Sep. 30, 2012 Maximum Accounting Standards Update 2010-26
Change in Accounting Estimate [Line Items] |  |  |  |  |  |  |
Increase in deferred policy acquisition costs |  | $ 68,656 | $ 52,849 |  |  | $ 8,000 | $ 10,000
Previously deferrable acquisition cost, expense recognized | $ 2,000 | $ 5,600 |  | $ 1,300 | $ 7,600 |  |

X
- Definition Expense of previously deferred cost under current accounting literature + References No definition available. + Details
Name: | afsi_ExpenseRecognizedOfPreviouslyDeferredCosts
Namespace Prefix: | afsi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_ChangeInAccountingEstimateLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The increase (decrease) during the reporting period in the balance sheet value of capitalized sales costs that are associated with acquiring a new insurance customers. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585 + Details
Name: | us-gaap_IncreaseDecreaseInDeferredPolicyAcquisitionCosts
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration