XML 52 R46.htm IDEA: XBRL DOCUMENT
v3.24.2

Fair Value Measurements - Schedule of Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands | Jun. 30, 2024 | Dec. 31, 2023
--- | --- | ---
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturity securities - available-for-sale, at fair value (amortized cost $299,652, allowance for credit losses of $0 in 2024 and amortized cost $326,171, allowance for credit losses of $0 in 2023) | $ 287,589 | $ 317,064
Equity securities, at fair value (cost $36,019 and $44,046 in 2024 and 2023, respectively) | 53,839 | 57,147
Fair Value, Measurements, Recurring [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturity securities - available-for-sale, at fair value (amortized cost $299,652, allowance for credit losses of $0 in 2024 and amortized cost $326,171, allowance for credit losses of $0 in 2023) | 287,589 | 317,064
Total | 341,428 | 374,211
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturity securities - available-for-sale, at fair value (amortized cost $299,652, allowance for credit losses of $0 in 2024 and amortized cost $326,171, allowance for credit losses of $0 in 2023) | 13,654 | 13,671
Total | 67,493 | 70,818
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturity securities - available-for-sale, at fair value (amortized cost $299,652, allowance for credit losses of $0 in 2024 and amortized cost $326,171, allowance for credit losses of $0 in 2023) | 273,935 | 303,393
Total | 273,935 | 303,393
Fair Value, Measurements, Recurring [Member] | States and Political Subdivisions [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturity securities - available-for-sale, at fair value (amortized cost $299,652, allowance for credit losses of $0 in 2024 and amortized cost $326,171, allowance for credit losses of $0 in 2023) | 117,889 | 131,895
Fair Value, Measurements, Recurring [Member] | States and Political Subdivisions [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturity securities - available-for-sale, at fair value (amortized cost $299,652, allowance for credit losses of $0 in 2024 and amortized cost $326,171, allowance for credit losses of $0 in 2023) | 117,889 | 131,895
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturity securities - available-for-sale, at fair value (amortized cost $299,652, allowance for credit losses of $0 in 2024 and amortized cost $326,171, allowance for credit losses of $0 in 2023) | 151,700 | 166,753
Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturity securities - available-for-sale, at fair value (amortized cost $299,652, allowance for credit losses of $0 in 2024 and amortized cost $326,171, allowance for credit losses of $0 in 2023) | 151,700 | 166,753
Fair Value, Measurements, Recurring [Member] | U.S. Agency-Based Mortgage-Backed Securities [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturity securities - available-for-sale, at fair value (amortized cost $299,652, allowance for credit losses of $0 in 2024 and amortized cost $326,171, allowance for credit losses of $0 in 2023) | 4,346 | 4,745
Fair Value, Measurements, Recurring [Member] | U.S. Agency-Based Mortgage-Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturity securities - available-for-sale, at fair value (amortized cost $299,652, allowance for credit losses of $0 in 2024 and amortized cost $326,171, allowance for credit losses of $0 in 2023) | 4,346 | 4,745
Fair Value, Measurements, Recurring [Member] | U.S. Treasury Securities [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturity securities - available-for-sale, at fair value (amortized cost $299,652, allowance for credit losses of $0 in 2024 and amortized cost $326,171, allowance for credit losses of $0 in 2023) | 13,654 | 13,671
Fair Value, Measurements, Recurring [Member] | U.S. Treasury Securities [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Fixed maturity securities - available-for-sale, at fair value (amortized cost $299,652, allowance for credit losses of $0 in 2024 and amortized cost $326,171, allowance for credit losses of $0 in 2023) | 13,654 | 13,671
Fair Value, Measurements, Recurring [Member] | Common Stock [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Equity securities, at fair value (cost $36,019 and $44,046 in 2024 and 2023, respectively) | 53,839 | 57,147
Fair Value, Measurements, Recurring [Member] | Common Stock [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Equity securities, at fair value (cost $36,019 and $44,046 in 2024 and 2023, respectively) | $ 53,839 | $ 57,147

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 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 -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (aa) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481800/320-10-50-2 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481830/320-10-45-1 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 942 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(6)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org//1943274/2147479130/326-30-45-1 + 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), classified as current. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(2)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Subparagraph (f) -Publisher FASB -URI https://asc.fasb.org//1943274/2147483467/210-10-45-1 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 825 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 1A -Publisher FASB -URI https://asc.fasb.org//1943274/2147482736/825-10-45-1A + Details
Name: | us-gaap_EquitySecuritiesFvNi
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482106/820-10-50-2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482106/820-10-50-2 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482106/820-10-50-3 + Details
Name: | us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=us-gaap_CommonStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |