XML 111 R95.htm IDEA: XBRL DOCUMENT v3.3.1.900

Concentration of Operations - Net Premiums Earned for the Top Ten States (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule Of Premiums Earned Net By Segment [Line Items]
Premiums earned	$ 95,034	$ 90,504	$ 95,569	$ 94,787	$ 97,070	$ 95,928	$ 93,516	$ 89,233	$ 375,894	$ 375,747	$ 329,983
Premium earned percentage									100.00%	100.00%	100.00%
Georgia [Member]
Schedule Of Premiums Earned Net By Segment [Line Items]
Premiums earned									$ 40,497	$ 36,761	$ 30,096
Premium earned percentage									10.80%	9.80%	9.10%
Louisiana [Member]
Schedule Of Premiums Earned Net By Segment [Line Items]
Premiums earned									$ 38,874	$ 47,643	$ 42,110
Premium earned percentage									10.30%	12.70%	12.80%
Pennsylvania [Member]
Schedule Of Premiums Earned Net By Segment [Line Items]
Premiums earned									$ 36,294	$ 35,488	$ 28,880
Premium earned percentage									9.70%	9.40%	8.80%
Florida [Member]
Schedule Of Premiums Earned Net By Segment [Line Items]
Premiums earned									$ 24,792	$ 20,691	$ 12,950
Premium earned percentage									6.60%	5.50%	3.90%
Illinois [Member]
Schedule Of Premiums Earned Net By Segment [Line Items]
Premiums earned									$ 23,285	$ 20,606	$ 18,445
Premium earned percentage									6.20%	5.50%	5.60%
North Carolina [Member]
Schedule Of Premiums Earned Net By Segment [Line Items]
Premiums earned									$ 20,062	$ 20,872	$ 21,019
Premium earned percentage									5.30%	5.60%	6.40%
Virginia [Member]
Schedule Of Premiums Earned Net By Segment [Line Items]
Premiums earned									$ 15,656	$ 16,764	$ 15,751
Premium earned percentage									4.20%	4.50%	4.80%
Texas [Member]
Schedule Of Premiums Earned Net By Segment [Line Items]
Premiums earned									$ 15,226	$ 14,846	$ 14,949
Premium earned percentage									4.00%	4.00%	4.50%
Minnesota [Member]
Schedule Of Premiums Earned Net By Segment [Line Items]
Premiums earned									$ 14,618	$ 13,159	$ 10,470
Premium earned percentage									3.90%	3.50%	3.20%
Oklahoma [Member]
Schedule Of Premiums Earned Net By Segment [Line Items]
Premiums earned									$ 13,420	$ 16,599	$ 17,473
Premium earned percentage									3.60%	4.40%	5.30%
All Others [Member]
Schedule Of Premiums Earned Net By Segment [Line Items]
Premiums earned									$ 133,170	$ 132,318	$ 117,840
Premium earned percentage									35.40%	35.10%	35.60%

X

- Definition

Premiums Earned Percentage

+ References

No definition available.

+ Details

Name:	amsf_PremiumsEarnedPercentage
Namespace Prefix:	amsf_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Schedule Of Premiums Earned Net By Segment [Line Items]

+ References

No definition available.

+ Details

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

X

- Definition

Amount, after premiums ceded to other entities and premiums assumed by the entity, of premiums earned.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.1)
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 605
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.13(c))
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 235
-Section S99
-Paragraph 2
-Subparagraph (SX 210.12-17)
-URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e574992-122915

+ Details

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

X

- Details

Name:	us-gaap_StatementGeographicalAxis=stpr_GA
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementGeographicalAxis=stpr_LA
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementGeographicalAxis=stpr_PA
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementGeographicalAxis=stpr_FL
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementGeographicalAxis=stpr_IL
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementGeographicalAxis=stpr_NC
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementGeographicalAxis=stpr_VA
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementGeographicalAxis=stpr_TX
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementGeographicalAxis=stpr_MN
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementGeographicalAxis=stpr_OK
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementGeographicalAxis=amsf_AllOtherStatesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: