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Investment Securities - Proceeds from the call of held-to-maturity investment securities (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2022 | Sep. 30, 2021 | Sep. 30, 2022 | Sep. 30, 2021
Investment Securities |  |  |  |
Proceeds | $ 101 | $ 348 | $ 827 | $ 1,763
Realized gains |  | $ 11 |  | $ 11

X
- Definition Amount of gain on sale of investment in debt security measured at amortized cost (held-to-maturity), including other-than-temporary impairment (OTTI). + References No definition available. + Details
Name: | alrs_DebtSecuritiesHeldToMaturitySoldRealizedGain
Namespace Prefix: | alrs_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The cash inflow associated with the sale or calls of securities that had been designated as held-to-maturity. + References No definition available. + Details
Name: | alrs_ProceedsFromSaleOrCallsOfHeldToMaturitySecurities
Namespace Prefix: | alrs_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_InvestmentsDebtAndEquitySecuritiesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration