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Tax Credit Investments - Tax credits (Details) - USD ($) $ in Thousands | Mar. 31, 2023 | Dec. 31, 2022
--- | --- | ---
Tax Credit Investments [Line items] |  |
Investment | $ 17,906 | $ 17,906
Unfunded Commitment | 15,471 | 15,559
Proportional amortization |  |
Tax Credit Investments [Line items] |  |
Investment | 17,906 | 17,906
Unfunded Commitment | $ 15,471 | $ 15,559

X
- Definition Amount of gross low-income housing tax credit, before amortization expense. + References No definition available. + Details
Name: | alrs_LowIncomeHousingTaxCreditGross
Namespace Prefix: | alrs_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition The amount of low income housing tax credit of unfunded commitment. + References No definition available. + Details
Name: | alrs_LowIncomeHousingTaxCreditUnfundedCommitment
Namespace Prefix: | alrs_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Tax Credit Investments [Line items] + References No definition available. + Details
Name: | alrs_TaxCreditInvestmentsLineItems
Namespace Prefix: | alrs_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | alrs_AccountingMethodAxis=alrs_ProportionalAmortizationMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |