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Restrictions on Cash and Due from Banks (Details) - USD ($) $ in Thousands | Dec. 31, 2022 | Dec. 31, 2021
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Restrictions on Cash and Due from Banks |  |
Amount of minimum average reserve balances required to be maintained | $ 0 | $ 0
Balances at the Federal Reserve Bank and other financial institutions | $ 28,000 | $ 224,400

X
- Definition Represents the amount of minimum average reserve balances required to be maintained. + References No definition available. + Details
Name: | alrs_AmountOfMinimumAverageReserveBalancesRequiredToBeMaintained
Namespace Prefix: | alrs_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition N/A + References No definition available. + Details
Name: | alrs_RestrictionsOnCashAndDueFromBanksAbstract
Namespace Prefix: | alrs_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of cash subject to withdrawal restrictions, restricted deposits held as compensating balances, and cash and securities segregated in compliance with regulations (such as cash deposited in a special reserve account for the exclusive benefit of customers). + References No definition available. + Details
Name: | us-gaap_CashAndSecuritiesSegregatedUnderFederalAndOtherRegulations
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant