v2.4.0.6

Acquisitions - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		1 Months Ended	3 Months Ended	9 Months Ended	1 Months Ended		3 Months Ended	9 Months Ended				9 Months Ended
	Sep. 30, 2012 Cnh Capital Insurance Agencies	Jul. 12, 2012 Cnh Capital Insurance Agencies	Dec. 31, 2011 Builders and Trades Men's Insurance Services Inc	Sep. 30, 2012 Builders and Trades Men's Insurance Services Inc	Sep. 30, 2012 Builders and Trades Men's Insurance Services Inc	Dec. 31, 2011 Builders and Trades Men's Insurance Services Inc Renewal Rights	Dec. 31, 2011 Builders and Trades Men's Insurance Services Inc Distribution Networks	Sep. 30, 2012 Majestic	Sep. 30, 2012 Majestic	Sep. 30, 2011 Majestic	Jun. 01, 2011 Majestic	Sep. 30, 2012 Majestic Distribution Networks and Trademarks	Sep. 30, 2012 Majestic Distribution Networks	Sep. 30, 2012 Majestic Trademarks	Sep. 30, 2011 Majestic Maximum
Business Acquisition [Line Items]
Cost of acquisition		$ 34,000
Preliminary purchase price recorded by the company		34,000
Assigned to intangible assets		33,000
Advance payment made for acquisition			5,000
Business acquisition profitability measurement period			4 years
Business acquisition, purchase price			47,000
Business acquisition, goodwill and intangibles			59,000
Acquired finite-lived intangible assets, weighted average useful life						11 years	17 years						13 years	2 years
Liability related to an unfavorable lease assumed			2,400					390	390
Fee revenue recorded during acquisition				3,600	14,600
Liability for losses and loss adjustment expenses gross										331,660
Percentage of unearned premium reserve assumed										100.00%
Unearned premium reserve amount assumed										25,997
Cash and investments received										224,532
Reserve deficiency										26,000
Reinsurance recoverable										51,715
Percentage of net earned premium paid to acquiree															3.00%
Required loss ratio in the three year period commencing on the losing date															65.00%
Insurance premiums recorded since acquisition date	4,400			24,000	52,000			26,000	73,500
Acquired finite-lived intangible assets												3,870
Liability related to profit sharing provision								815	815
Fair value of loss reserve											$ 328,905

X

- Definition

Accrued Loss Reserves

+ References

No definition available.

+ Details

Name:	afsi_AccruedLossReserves
Namespace Prefix:	afsi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Business Acquisition, Initial Purchase Price

+ References

No definition available.

+ Details

Name:	afsi_BusinessAcquisitionInitialPurchasePrice
Namespace Prefix:	afsi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Business Acquisition, Percentage of Unearned Premium Reserve Assumed

+ References

No definition available.

+ Details

Name:	afsi_BusinessAcquisitionPercentageOfUnearnedPremiumReserveAssumed
Namespace Prefix:	afsi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Business Acquisition, Profitability Measurement Period

+ References

No definition available.

+ Details

Name:	afsi_BusinessAcquisitionProfitabilityMeasurementPeriod
Namespace Prefix:	afsi_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Business Acquisition, Purchase Price Allocation, Cash and Investments

+ References

No definition available.

+ Details

Name:	afsi_BusinessAcquisitionPurchasePriceAllocationCashAndInvestments
Namespace Prefix:	afsi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Business Acquisition, Purchase Price Allocation, Intangible Assets and Goodwill

+ References

No definition available.

+ Details

Name:	afsi_BusinessAcquisitionPurchasePriceAllocationIntangibleAssetsAndGoodwill
Namespace Prefix:	afsi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Business Acquisition Purchase Price Allocation Loss and Loss Adjustment Expense

+ References

No definition available.

+ Details

Name:	afsi_BusinessAcquisitionPurchasePriceAllocationLossAndLossAdjustmentExpense
Namespace Prefix:	afsi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Business Acquisition Purchase Price Allocation Reinsurance Recoverable

+ References

No definition available.

+ Details

Name:	afsi_BusinessAcquisitionPurchasePriceAllocationReinsuranceRecoverable
Namespace Prefix:	afsi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Business Acquisition, Purchase Price Allocation, Reserve Deficiency

+ References

No definition available.

+ Details

Name:	afsi_BusinessAcquisitionPurchasePriceAllocationReserveDeficiency
Namespace Prefix:	afsi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Business Acquisition Purchase Price Allocation Unearned Premium

+ References

No definition available.

+ Details

Name:	afsi_BusinessAcquisitionPurchasePriceAllocationUnearnedPremium
Namespace Prefix:	afsi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Business Acquisition Revenue Recorded

+ References

No definition available.

+ Details

Name:	afsi_BusinessAcquisitionRevenueRecorded
Namespace Prefix:	afsi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Loss Ratio

+ References

No definition available.

+ Details

Name:	afsi_LossRatio
Namespace Prefix:	afsi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Percentage of Net Earned Premium

+ References

No definition available.

+ Details

Name:	afsi_PercentageOfNetEarnedPremium
Namespace Prefix:	afsi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

The aggregate amount assigned to a major class of finite-lived intangible assets acquired either individually or as part of a group of assets (in either an asset acquisition or business combination). A major class is composed of intangible assets that can be grouped together because they are similar, either by their nature or by their use in the operations of a company.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 1

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=7658586&loc=d3e16265-109275



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 142

-Paragraph 44

-Subparagraph a(1)

-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

Name:	us-gaap_AcquiredFiniteLivedIntangibleAssetAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, 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 350

-SubTopic 30

-Section 50

-Paragraph 1

-Subparagraph (a)(3)

-URI http://asc.fasb.org/extlink&oid=7658586&loc=d3e16265-109275

+ Details

Name:	us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The total cost of the acquired entity including the cash paid to shareholders of acquired entities, fair value of debt and equity securities issued to shareholders of acquired entities, the fair value of the liabilities assumed, and direct costs of the acquisition.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141

-Paragraph 51

-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

Name:	us-gaap_BusinessAcquisitionCostOfAcquiredEntityPurchasePrice
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Details

Name:	us-gaap_BusinessAcquisitionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Amount of acquisition cost of a business combination allocated to other liabilities not separately disclosed in the balance sheet.

+ References

No definition available.

+ Details

Name:	us-gaap_BusinessAcquisitionPurchasePriceAllocationOtherLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

The amount of acquisition cost of a business combination allocated to unfavorable contracts assumed from the acquired entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141

-Paragraph 37

-Subparagraph k

-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 Emerging Issues Task Force (EITF)

-Number 04-1

-Paragraph 4, 8

-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

Name:	us-gaap_BusinessAcquisitionPurchasePriceAllocationUnfavorableContractAccrual
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

This element represents the acquisition-date fair value of the total consideration transferred which consists of the sum of the acquisition-date fair values of the assets transferred by the acquirer, the liabilities incurred by the acquirer to former owners of the acquiree, and the equity interests issued by the acquirer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141R

-Paragraph 68

-Subparagraph f

-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 Statement of Financial Accounting Standard (FAS)

-Number 141R

-Paragraph 39, 40

-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 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 30

-Section 30

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6613-128477



Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 30

-Section 30

-Paragraph 7

-URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6578-128477



Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 30

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7488404&loc=d3e6927-128479

+ Details

Name:	us-gaap_BusinessCombinationConsiderationTransferred
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

This element represents the amount of revenue of the acquiree since the acquisition date included in the consolidated income statement for the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(1)

-URI http://asc.fasb.org/extlink&oid=7659399&loc=d3e1392-128463



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141R

-Paragraph 68

-Subparagraph r(1)

-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

Name:	us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

The amount of identifiable intangible assets recognized as of the acquisition date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141R

-Paragraph 12, 13, 14, 20, A107

-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 805

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6910749&loc=d3e4845-128472



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 55

-Paragraph 37

-URI http://asc.fasb.org/extlink&oid=9154965&loc=d3e2207-128464



Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141R

-Paragraph 68

-Subparagraph i

-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

Name:	us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Net amount recognized for aggregate assets, including goodwill, in excess of or less than the aggregate liabilities assumed (also referred to as net assets acquired). This amount may also be viewed as incremental amount of equity that the consolidated entity (including the portion attributable to a noncontrolling interest) will recognize as a result of the business combination.

+ References

No definition available.

+ Details

Name:	us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant