XML 46 R76.htm IDEA: XBRL DOCUMENT v2.4.1.9

Loss and Loss Adjustment Expenses - Summary Exposures to Various Asbestos Related Claims (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Asbestos Claims [Line Items]
Balance, beginning of period	$ 614,557us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense	$ 570,450us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense	$ 538,214us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense
Incurred losses and LAE during the current year	244,916us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1	228,973us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1	219,903us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1
Loss and LAE payments	(52,848)us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidCurrentYear1	(51,169)us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidCurrentYear1	(50,423)us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidCurrentYear1
Balance, end of period	687,602us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense	614,557us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense	570,450us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense
Asbestos Issue [Member]
Asbestos Claims [Line Items]
Balance, beginning of period	219us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense / us-gaap_LiabilityForCatastropheClaimsByCatastrophicEventAxis = us-gaap_AsbestosIssueMember	167us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense / us-gaap_LiabilityForCatastropheClaimsByCatastrophicEventAxis = us-gaap_AsbestosIssueMember
Incurred losses and LAE during the current year	882us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1 / us-gaap_LiabilityForCatastropheClaimsByCatastrophicEventAxis = us-gaap_AsbestosIssueMember	53us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1 / us-gaap_LiabilityForCatastropheClaimsByCatastrophicEventAxis = us-gaap_AsbestosIssueMember	168us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1 / us-gaap_LiabilityForCatastropheClaimsByCatastrophicEventAxis = us-gaap_AsbestosIssueMember
Loss and LAE payments	(282)us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidCurrentYear1 / us-gaap_LiabilityForCatastropheClaimsByCatastrophicEventAxis = us-gaap_AsbestosIssueMember	(1)us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidCurrentYear1 / us-gaap_LiabilityForCatastropheClaimsByCatastrophicEventAxis = us-gaap_AsbestosIssueMember	(1)us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidCurrentYear1 / us-gaap_LiabilityForCatastropheClaimsByCatastrophicEventAxis = us-gaap_AsbestosIssueMember
Balance, end of period	$ 819us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense / us-gaap_LiabilityForCatastropheClaimsByCatastrophicEventAxis = us-gaap_AsbestosIssueMember	$ 219us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense / us-gaap_LiabilityForCatastropheClaimsByCatastrophicEventAxis = us-gaap_AsbestosIssueMember	$ 167us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense / us-gaap_LiabilityForCatastropheClaimsByCatastrophicEventAxis = us-gaap_AsbestosIssueMember

X

- Details

Name:	amsf_AsbestosClaimsLineItems
Namespace Prefix:	amsf_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The amount needed to reflect the estimated ultimate cost of settling claims relating to insured events that have occurred on or before the balance sheet date, whether or not reported to the insurer at that date.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 40

-Section 50

-Paragraph 3

-Subparagraph (a),(b),(c)

-URI http://asc.fasb.org/extlink&oid=6482485&loc=d3e14764-158437

+ Details

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

X

- Definition

Amount of payments to settle claims incurred in the current period and related claims settlement costs.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 40

-Section 50

-Paragraph 3

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6482485&loc=d3e14764-158437

+ Details

Name:	us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidCurrentYear1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Amount of expense for claims incurred and costs incurred in the claim settlement process.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 40

-Section 50

-Paragraph 3

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6482485&loc=d3e14764-158437

+ Details

Name:	us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Details

Name:	us-gaap_LiabilityForCatastropheClaimsByCatastrophicEventAxis=us-gaap_AsbestosIssueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: