XML 63 R50.htm IDEA: XBRL DOCUMENT v3.10.0.1

Investments - Gross Unrealized Gains and Losses and Cost or Amortized Cost and Fair Value of Investments Classified as Available-for-Sale (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Investment [Line Items]
Fixed maturity, Cost or Amortized Cost	$ 479,772	$ 461,236
Fixed maturity, Gross Unrealized Gains	3,758	7,072
Fixed maturity, Gross Unrealized Losses	(4,800)	(2,714)
Fixed maturity, Fair Value	478,730	465,594
Equity securities, Cost or Amortized Cost	19,962	8,503
Equity securities, Gross Unrealized Gains	30	779
Equity securities, Gross Unrealized Losses	(1,341)
Equity securities, Fair Value	18,651	9,282
Totals, Cost or Amortized Cost		469,739
Totals, Gross Unrealized Gains		7,851
Totals, Gross Unrealized Losses		(2,714)
Totals, Fair Value		474,876
States and Political Subdivisions [Member]
Investment [Line Items]
Fixed maturity, Cost or Amortized Cost	231,848	244,898
Fixed maturity, Gross Unrealized Gains	3,515	6,819
Fixed maturity, Gross Unrealized Losses	(2,118)	(577)
Fixed maturity, Fair Value	233,245	251,140
Corporate Bonds [Member]
Investment [Line Items]
Fixed maturity, Cost or Amortized Cost	173,904	130,210
Fixed maturity, Gross Unrealized Gains	243	224
Fixed maturity, Gross Unrealized Losses	(933)	(212)
Fixed maturity, Fair Value	173,214	130,222
U.S. Agency-Based Mortgage-Backed Securities [Member]
Investment [Line Items]
Fixed maturity, Cost or Amortized Cost	12,835	18,813
Fixed maturity, Gross Unrealized Losses	(320)	(799)
Fixed maturity, Fair Value	12,515	18,014
U.S. Treasury Securities and Obligations of U.S. Government Agencies [Member]
Investment [Line Items]
Fixed maturity, Cost or Amortized Cost	61,185	67,315
Fixed maturity, Gross Unrealized Gains		29
Fixed maturity, Gross Unrealized Losses	(1,429)	(1,126)
Fixed maturity, Fair Value	$ 59,756	$ 66,218

X

- Definition

Available for sale securities debt securities and equity securities Fv-Ni.

+ References

No definition available.

+ Details

Name:	amsf_AvailableForSaleSecuritiesDebtSecuritiesAndEquitySecuritiesFvNi
Namespace Prefix:	amsf_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Available for sale securities debt securities and equity Securities fair value net income accumulated gross unrealized gain before tax.

+ References

No definition available.

+ Details

Name:	amsf_AvailableForSaleSecuritiesDebtSecuritiesAndEquitySecuritiesFvNiAccumulatedGrossUnrealizedGainBeforeTax
Namespace Prefix:	amsf_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Available for sale securities debt securities and equity Securities fair value net income accumulated gross unrealized loss before tax.

+ References

No definition available.

+ Details

Name:	amsf_AvailableForSaleSecuritiesDebtSecuritiesAndEquitySecuritiesFvNiAccumulatedGrossUnrealizedLossBeforeTax
Namespace Prefix:	amsf_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Available for sale securities debt securities and equity securities fvni amortized cost basis.

+ References

No definition available.

+ Details

Name:	amsf_AvailableForSaleSecuritiesDebtSecuritiesAndEquitySecuritiesFvNiAmortizedCostBasis
Namespace Prefix:	amsf_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Equity securities fair value net income gross unrealized gain.

+ References

No definition available.

+ Details

Name:	amsf_EquitySecuritiesFvNiGrossUnrealizedGain
Namespace Prefix:	amsf_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Equity Securities fair value net income gross unrealized loss.

+ References

No definition available.

+ Details

Name:	amsf_EquitySecuritiesFvNiGrossUnrealizedLoss
Namespace Prefix:	amsf_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- References

No definition available.

+ Details

Name:	invest_InvestmentLineItems
Namespace Prefix:	invest_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

+ Details

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

X

- Definition

Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

+ Details

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

X

- Definition

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

+ Details

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

X

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

+ Details

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

X

- Definition

Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740

+ Details

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

X

- Definition

Cost of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). Excludes equity method investment and investment in equity security without readily determinable fair value.

+ References

No definition available.

+ Details

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

X

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_USTreasuryAndGovernmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: