XML 105 R94.htm IDEA: XBRL DOCUMENT
v3.25.0.1

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Commitments And Contingencies [Line Items] |  |  |
Operating lease, existence of option to extend | true |  |
Finance lease, existence of option to extend | true |  |
Rent expense | $ 0.1 | $ 0.1 | $ 0.1
Minimum [Member] |  |  |
Commitments And Contingencies [Line Items] |  |  |
Operating lease, remaining lease term | 1 month |  |
Finance lease, remaining lease term | 1 month |  |
Maximum [Member] |  |  |
Commitments And Contingencies [Line Items] |  |  |
Operating lease, remaining lease term | 49 months |  |
Finance lease, remaining lease term | 49 months |  |
Operating lease, options to extend lease term | 5 years |  |
Finance lease, options to extend lease term | 5 years |  |

X
- Definition Commitments And Contingencies [Line Items] + References No definition available. + Details
Name: | amsf_CommitmentsAndContingenciesLineItems
Namespace Prefix: | amsf_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Finance lease remaining lease term. + References No definition available. + Details
Name: | amsf_FinanceLeaseRemainingLeaseTerm
Namespace Prefix: | amsf_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Operating lease remaining lease term. + References No definition available. + Details
Name: | amsf_OperatingLeaseRemainingLeaseTerm
Namespace Prefix: | amsf_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Indicates (true false) whether lessee has option to extend finance lease. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 842 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (a)(3) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478964/842-20-50-3 + Details
Name: | us-gaap_LesseeFinanceLeaseExistenceOfOptionToExtend
Namespace Prefix: | us-gaap_
Data Type: | xbrli:booleanItemType
Balance Type: | na
Period Type: | duration

X
- Definition Term of lessee's finance lease renewal, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 842 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (a)(3) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478964/842-20-50-3 + Details
Name: | us-gaap_LesseeFinanceLeaseRenewalTerm1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | instant

X
- Definition Indicates (true false) whether lessee has option to extend operating lease. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 842 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (a)(3) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478964/842-20-50-3 + Details
Name: | us-gaap_LesseeOperatingLeaseExistenceOfOptionToExtend
Namespace Prefix: | us-gaap_
Data Type: | xbrli:booleanItemType
Balance Type: | na
Period Type: | duration

X
- Definition Term of lessee's operating lease renewal, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 842 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (a)(3) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478964/842-20-50-3 + Details
Name: | us-gaap_LesseeOperatingLeaseRenewalTerm
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount of operating lease expense. Excludes sublease income. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 842 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 4 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479041/842-20-45-4 + Details
Name: | us-gaap_OperatingLeaseExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |